Challenges in Coalition Unconventional Warfare: The Allied Campaign in Yugoslavia, 1941–1945

By J. Darren Duke, Rex L. Phillips, and Christopher J. Conover Joint Force Quarterly 75


Sept. 30, 2014 — During World War II, operatives and military advisors of the British Special Operations Executive (SOE) and the American Office of Strategic Services (OSS), which was a precursor to both the current Central Intelligence Agency and U.S. Special Forces, conducted a challenging unconventional warfare (UW) campaign against the Axis forces with and through guerrilla resistance elements in Yugoslavia. The resistance movement effectively fixed in place 35 German and Italian divisions, consisting of roughly 660,000 soldiers in the western Balkan region during 1941–1945.1 This campaign rendered them strategically irrelevant by preventing their use in other theaters. The combined United Kingdom (UK)–United States (U.S.) contingent achieved this effect with never more than 100 Allied personnel on the ground in the denied area. The number of Axis personnel killed in the Balkans is estimated at 450,000.2 This extremely favorable force ratio and its associated effects commend UW as a low-cost, high-reward method of warfare.

Marshal Josip Tito (right) stands with his Cabinet Ministers and Supreme Staff at his mountain headquarters in Yugoslavia on May 14, 1944 (Imperial War Museum)

Marshal Josip Tito (right) stands with his Cabinet Ministers and Supreme Staff at his mountain headquarters in Yugoslavia on May 14, 1944 (Imperial War Museum)

Although ultimately successful, the campaign experienced difficulties. British and American policymakers, primarily President Franklin D. Roosevelt and Prime Minister Winston Churchill, chose with great risk near-term military goals over long-term postwar political strategic interests. Failures in operations security, differences in policy goals, difficulties in command relationships, and disparities in talent and skill among Allied personnel often strained the British-American relationship at multiple levels. Clandestine operatives on the ground inside Yugoslavia dealt with an increasingly vicious civil war among factions within the resistance movements that was rooted in longstanding political and ethnic differences. Contemporary policymakers and UW planners considering unconventional options can benefit from an examination of these challenges, experiences, and lessons learned from the Balkans Campaign of World War II.

Unconventional warfare is activities conducted to enable a resistance movement or insurgency to coerce, disrupt, or overthrow a government or occupying power by operating through or with an underground, auxiliary, or guerrilla force in a denied area.3 Special operations forces (SOF) conduct and support unconventional warfare. U.S. Army Special Forces, Green Berets, are the lead SOF Service component for its doctrine and conduct, while other Service components of U.S. Special Operations Command are tasked with conducting operations in support of UW efforts. Currently, no doctrine for joint or combined UW operations exists. However, history shows us that combined UW not only is possible, but also can be highly successful, even if fraught with challenges. The combined UK-U.S. UW campaign in the former Yugoslavia offers several important lessons that should inform and help shape continued efforts to improve UW doctrine.

The Balkan Campaign

Formed out of the upheavals of the Balkan wars of the early 1900s and the fallout from World War I, Yugoslavia was a patchwork state cobbled together by treaty and riven by political and ethnic strife. In the spring of 1941, when Adolf Hitler realized that Yugoslavia’s weak cohesion as a state would not allow him to keep it in the Tripartite Pact and to protect his southern flank in preparation for his invasion of Soviet Russia,4 he ordered the German-led blitzkrieg attack by Axis forces on April 6, 1941, which brought Yugoslavia into the war. Organized Yugoslavian military resistance rapidly evaporated, and the government capitulated after only 11 days. Armed guerrilla attacks on German and Italian units began in earnest by early July.5 These attacks—eventually recognized as the most successful guerrilla movement in occupied Europe—created sufficient concern within the German government that counterguerrilla operations were conducted to address the threat. These resulted in severe reprisals against Yugoslavian civilians as early as October 1941.6

Early in the war, Churchill expressed a desire to “set Europe ablaze.” When he learned of the resistance operations, he directed the SOE to assess the possibility of providing support to these groups to open up an additional front against the Axis regimes across Europe. The SOE and British secret service had access to an array of regional experts with language abilities and operational skills to provide this assessment. As early as 1939, the British government developed a well-established clandestine presence in Yugoslavia that remained active until the Axis invasion in April 1941.7 One of these former operatives, and an excellent example of the British talent, was Captain D.T. “Bill” Hudson.

Bill Hudson arrived in Yugoslavia in 1935 to manage an antimony mine. By 1938, he was fluent in Serbo-Croatian, joined the British secret service, and recruited a network of saboteurs in Croatia for operations against Axis shipping along the Dalmatian coast. Inserted into Yugoslavia by submarine on September 20, 1941, his mission was to determine whom the British government could trust and how it could help disrupt the Axis occupation forces.8

His initial findings were not encouraging; old ethnic animosities and new political differences deeply divided the two primary Yugoslavian resistance groups. A Serbian military officer named Dragoljub “Draža” Mihailovic led disparate elements of varying loyalty to the Yugoslavian monarchy-in-exile called Chetniks. Josip Broz Tito led a second group of communist resistance units known as the Partisans. These two groups fought each other in a fierce civil war. British intelligence and the SOE took 2 years to determine which side to back against the Axis powers.

By the summer of 1943, SOE field reports and signals intelligence9 convinced Churchill to suspend support to the Chetniks and to expand cooperation with and support of Tito and his Partisans. This decision was highly controversial and taken with a clear realization of the impact on the postwar political order in Europe. The suspension of support for the Chetniks meant the abandonment of a government previously recognized by the UK and a monarch related to British King George VI. Moreover, it meant the tacit recognition of a movement with unambiguous intentions of establishing a communist state in postwar Yugoslavia. No other country where the SOE and OSS facilitated resistance and guerrilla operations presented as severe a challenge in negotiating the deep divide between resistance factions or in weighing the risks of postwar interests in favor of near-term strategic ends.

Sigfried Uiberreither, Martin Bormann, Adolf Hitler, and Otto Dietrich in Maribor, April 26, 1941 (Deutsches Bundesarchiv)

Sigfried Uiberreither, Martin Bormann, Adolf Hitler, and Otto Dietrich in Maribor, April 26, 1941 (Deutsches Bundesarchiv)

In the United States, OSS Director Brigadier General William J. Donovan began to consider strategies in the Balkans designed to fracture the Tripartite Pact. Nevertheless, none of these efforts proved successful. With British facilitation, Donovan had visited Belgrade in January of 1941 and communicated to both the Yugoslavian government and its armed forces that the United States was ready to support resistance to German aggression.10 This offer was rebuffed. In fact, during that very visit, a Yugoslavian delegation was putting the ink on an agreement to join the Axis Powers. In the end, all of these efforts came to naught in the wake of the Axis invasion later in April 1941.

The separate streams of Allied interest came together again during summer and fall of 1943 after the fall of Benito Mussolini. With Italy falling away from the Axis, the Allies now had an opportunity to exploit the Balkan situation to their advantage by convincing Hitler that the Allied push into Europe might come via the central Mediterranean coast. Donovan received approval from the Combined Chiefs of Staff to initiate unconventional warfare operations in Yugoslavia in September 1943. Simultaneously, Churchill authorized SOE to expand contacts with Tito and his Partisans and to assess their capabilities and requirements. The OSS provided operatives to this UK-led effort as well as attempting, albeit unsuccessfully, to conduct its own operations.

Command of the UW effort in the Balkans was given to Brigadier Fitzroy MacLean. MacLean had no previous military training prior to World War II but had served the British Foreign Office during the 1930s as a diplomat in the British embassy in Moscow. Through his experiences in the Soviet Union, which included reporting on the purges and show trials under Joseph Stalin and extended solo travel into the Caucasus and Central Asia, MacLean developed a keen understanding of the communist movement, Eastern European culture, and political-military affairs in general. Upon the outbreak of the war, he resigned his diplomatic position and eventually found his way into the newly organized British Special Air Service, conducting raids and long-range reconnaissance against German and Italian forces in North Africa and then establishing a UW network in Tehran as a hedge against possible Nazi domination of Iran. This rare combination of experiences made MacLean the perfect man for the job.

Throughout 1944 and into mid-1945, the Allies established and operated numerous clandestine and expeditionary airfields, drop zones, and beach landing sites. Through these facilities, the SOE and OSS teams brought in tons of weapons, explosives, and ammunition directly to the subordinate Partisan formations. They provided training to Partisan units in demolitions, marksmanship, and tactics. Allied advisors accompanied Partisan forces on raids and sabotage missions against Axis lines of communication.11 During all of these activities, they provided detailed intelligence reports of the situation in Yugoslavia and conducted combined planning with the Yugoslavians for future operations and—with less success—unilateral efforts to establish agent networks in Austria for future UW missions within the Third Reich’s territory.12

National Tensions

The success in the Yugoslavian campaign was achieved in spite of forces and factors working against the Allied efforts. Allied pilots from America and Great Britain, Royal Navy ships, and submarines transported personnel and materiel with no regard for national origin or flag. OSS officers served as advisors to Partisan formations under orders from MacLean with loyalty and focus even to the point of ignoring operational proposals from OSS headquarters that threatened to distract them from the goal of helping the Partisans defeat the Axis.13 It is a testament to the leadership of the U.S. and Allied governments, the SOE and OSS, and the professionalism of the majority of field operatives and officers that none of these elements rose above the level of irritant against the goal of Axis defeat.

One of the most obvious sources of tension was the overwhelming disparity in the level of expertise in Balkan regional affairs, culture, and language possessed by the operatives on the ground. As noted above, the British possessed talented men such as Hudson and MacLean with deep regional and professional knowledge. To the contrary, the Americans lacked regional expertise and were almost solely dependent upon Yugoslavian or British translators to facilitate communications. This gap led to tensions between Allied personnel as British officers marginalized Americans by holding meetings in Serbo-Croatian—which the Americans could not speak—or forbidding unescorted American access to senior Yugoslavian leaders.14 The situation worsened over the course of time, particularly as UK and U.S. policy goals diverged toward the end of the war. The result was the eventual establishment of separate American and British missions just prior to the end of the war.15

A second source of national tension was the difference in organization and operational authorities adopted by the United States and UK. Fitzroy MacLean served not only as a military advisor and coordinator of Allied military support, but also as the direct emissary of the British government to Tito. He enjoyed direct access to Churchill and was personally consulted by the prime minister at major junctions in the decisionmaking process. American OSS operatives were limited in authorities to military technical advice and assistance only. William Donovan may have enjoyed frequent access to President Roosevelt, but he was still required to submit his plans for approval by General George Marshall as well as the State Department for all of his global operations.

A third and final source of tension for considerations of combined UW was the inevitable competition between waxing and waning global powers. By 1943, with the U.S. war effort in full swing, America’s rise to the status of global power was clearly under way. British prospects of preserving their empire, however, were less assured. Yet it was the British who, by virtue of at least two centuries of colonialism and imperialism, amassed the experience and human capital for influencing global affairs. America was the new kid on the block and was learning many of the hard lessons in the laboratory of global war, to include how to play the games of politics, espionage, and coalition warfare.

Donovan realized that the OSS was dependent on the British secret service to provide training in tradecraft and expertise for clandestine operations. He also knew that national self-interest would necessitate the United States striking out on its own. He did this on several occasions, drawing sharp criticisms from his former British mentors for the unskilled way the OSS attempted operations. To be fair, while the British evinced an attitude of imperial superiority and possible ethnic and religious bias against the OSS and Donovan personally,16 the Americans gave them plenty of reason to complain. The OSS headquarters that oversaw the early stages of the Balkan Campaign in Istanbul was penetrated by the German intelligence agency, the Abwehr, making the British unwilling to share sensitive information on their operations. Donovan also invested more hope in the advertised abilities of the Chetniks because he lacked talented officers such as Hudson and MacLean to give him solid assessments of their intentions and capacity. The return on this investment by the end of the war was poor, and the United States wasted time in the erroneous belief that the ancient internecine hatreds of the Balkans could be healed by Allied efforts. Had the Americans possessed a MacLean-like figure, they might have saved themselves the effort.

The British-American competition manifested itself in disputes over communications as Americans had to send their OSS traffic over SOE nets using SOE codes, limiting their ability to communicate in OSS channels only.17 Donovan himself was also rejected by Churchill as a potential commander of the Yugoslavian effort, was refused entry into the Yugoslav theater on occasion,18 and lacked access to Yugoslavian leaders, as previously noted. By the end of the war this competition developed to the point where, unbeknownst to British authorities, the OSS placed an agent in London who reported information on British government intentions toward Yugoslavia after the armistice.19 The special British-American relationship survived the war and far beyond, but it was clear that where the clandestine arts were concerned, “the cousins”—as Donovan liked to call them—had become an alliance of equals.

Strategic Choices and Risks

The thorniest of all the challenges facing the Allies in the conduct of the Yugoslavian campaign was the decision to support the Partisans. Tito was clearly a committed communist intent on establishing a postwar political order consistent with those beliefs. At the same time, he was a highly effective and tenacious guerrilla leader who attacked the Germans and their allies without hesitation. Whatever the decision, there would be second- and third-order consequences for Allied (particularly British) interests and for the future of the Yugoslavian peoples in the face of a communist revolutionary threat clearly intent on exploiting the political turmoil in liberated areas of Eastern Europe to its advantage.

William J. Donovan, director of the Office of Strategic Services, 1942–1945 (U.S. Army)

William J. Donovan, director of the Office of Strategic Services, 1942–1945 (U.S. Army)

Churchill’s final choice to suspend all support to Mihailovic and his Chetniks in favor of Tito and the Partisans was a conscious acceptance of risk to long-term interests of the democratic West in order to achieve a more rapid defeat of Nazi Germany. Although it is clear in historical hindsight that other factors may have mitigated this risk, such as MacLean’s excellent handling of relations with Tito, it must be remembered that at the time, there was at least one other course of action. An effort was proposed that sought to heal or at least ameliorate the Chetnik-Partisan rift by bringing the two groups under the Combined Allied Command. This course of action offered the possibility of avoiding any ceding of Yugoslavia to the Soviets after the war. Both of these options had their adherents among British and Americans alike and at multiple levels of command. The correctness of the decision can be measured by the result: The Partisans effectively used the support provided by the Allies to achieve the most critical campaign objectives. Additionally, Churchill’s recognition and assistance of Tito’s government contributed to the moderation exhibited by Tito toward the West during the Cold War.

Lessons for Future Efforts

The challenges associated with combined UW operations during World War II in the former Yugoslavia present today’s UW policymakers, planners, and practitioners with several relevant lessons for consideration. The first is the importance of precrisis intelligence and intelligence-sharing. Intelligence is critical to the success of any endeavor, but the breadth and specificity of intelligence required to support UW operations are unique challenges because the disciplines used to collect intelligence for UW require a long time to bear fruit. Unlike general military intelligence related to conventional operations, the admixture of political and cultural factors creates the need for detailed intelligence long before the crisis erupts. When considering coalition partners, an imbalance in each side’s ability either to participate in or conduct independent intelligence operations can create tension similar to that seen between the United States and UK throughout the campaign. The British superiority in intelligence operations, both in their pool of talent and the way they put their talent far forward into the denied area, gave them an advantage that bred envy and distrust, however well it may have been suppressed by Donovan and others in the OSS. The Americans, on the other hand, had little understanding of the areas required to conduct UW and had limited means to collect the intelligence to educate them. The OSS analysts were also kept in the United States, severely hampering their ability to bring their expertise and understanding to bear on day-to-day operations or to effectively support policymakers.

Fortunately, the United States and UK were committed to sharing intelligence with each other so that both governments were aware of developments achieved by the other. This sharing included sensitive sources and methods. The lesson here is that coalition members must develop ways to share the important information required for operational success promptly and in a way that builds confidence in the relationship. This level of sharing is built through commitment over time. The United States must develop mid- to long-term operational and intelligence assessments of likely areas of future operations long before crises arise and create intelligence networks and partnerships for effective intelligence-sharing in those potential areas of operation.

The second lesson for the future is the criticality of unity of command and the coordination of policy and plans. As the American subordination of OSS operatives to the SOE shows, the Allies were able to maintain an essentially unified command structure throughout the campaign until the very last stages of the war. The key to this success was the ability of both British and American leaders to suppress national and personal ambitions and to maintain the priority on the defeat of the Axis. All of this occurred under the steady and calm leadership of President Roosevelt, who recognized and ably measured the risks of pursuing unilateral American goals until the appropriate time. Consequently, he deferred to Churchill and the British as senior partners in the endeavor. Differing views were allowed and debate was encouraged, but serious threats to smooth operations were dealt with quickly by American leaders. Additionally, American leaders at the tactical level demonstrated the ability to avoid national agendas and diversions of time and effort on nonessential tasks. An excellent example of this focus is American Franklin Lindsay’s resistance to OSS proposals for propaganda operations in favor of supporting MacLean’s plan for facilitating Partisan lethal operations against the Nazis. The unity of command demonstrated by the Allies allowed for collegial planning that consequently allowed resources to flow efficiently to the decisive places on the battlefield.

The third lesson is the criticality of talent at the operational level for the art of balancing strategic choices and risk. Churchill’s decision to support the Partisans was confirmed by signal intercepts, but intelligence on Chetnik failures to act was only half the story. Without the reporting from men such as Hudson and MacLean, Churchill would not have known if there was any other resistance group worthy of support. Furthermore, the ability of those British SOE officers to provide useful insights on the military and security affairs within Yugoslavia was not developed at the Royal Military Academy at Sandhurst. In fact, none of these SOE officers had formal military training. On the American side, none of the operatives showed any indication of prior assessment and selection for this particular mission other than meeting the general OSS requirements. Many were sent because of their personal prewar ties to Donovan. OSS officers lacked education in strategy, and although a few possessed native language proficiency, they brought ethnic bias along with it,20 thus limiting their usefulness in some aspects. In UW campaigns, the political, strategic, and tactical considerations of warfare all converge at a single focal point. Those serving in the denied area at that point in time and space not only require technical military knowledge but also must possess the understanding of cultural, political, and social dynamics driving the conflict. Whether by personal acquaintance, reputation, or professional development in a vetted process, these UW operatives must have the confidence of senior policymakers who rely on their reporting to inform good strategic decisions. The British SOE clearly possessed all of these traits, and the success of the campaign rested on the personal qualifications of these extraordinary individuals. This demonstrates the veracity of the “SOF truths” that people are more important than hardware and that competent special operations forces cannot be created after an emergency occurs.

Closely related to this principle is the final lesson: the strategic benefit of tactical karma. While the controversy over Churchill’s decision to back the Partisans still lingers today and while many of Tito’s postwar actions in establishing and ruling communist Yugoslavia were inconsistent with previous promises, the rapport that SOE and OSS operatives established with their Partisan counterparts explains well Yugoslavia’s relative openness to the West during the Cold War. Shared privation and danger with the Partisans cemented ties already developed through national commitments. MacLean demonstrated many of the same strengths in his dealings with Tito and maintained this rapport when the relationship suffered due to political differences. These SOE and OSS men persuaded the Allies to expand aid and support Partisan operations. Their efforts paid off not only in defeating the German forces in the Balkans but also in engendering goodwill toward the West that endured well into the Cold War era.


If the United States is sincere in its expressed desire for increasing the burden-sharing among our international partners in military and security operations around the globe, every operating domain and method of warfare must come to grips with the complexities and caveats of operating across national boundaries. Because of the unique way that national policy, strategy, and tactical concerns come together in UW operations, this method of warfare, perhaps more than any other, requires the development of new ways of sharing intelligence, defining operational authorities, forging effective command structures, and building rapport within the coalition and with the indigenous guerrilla forces, undergrounds, and auxiliaries. The means to this end will be people: men and women with the right combination of skills, experiences, and courage in the spirit of MacLean, Hudson, Donovan, and many others.

Finally, if the United States is successful in increasing the burden borne by our allies and friends in future conflicts, then it is reasonable to conclude that America will conduct UW operations within coalitions. Furthermore, in spite of modern Americans being more globally aware than the World War II generation, pervasive media and information technologies will require the United States to partner with nations who can operate clandestinely in denied and politically sensitive areas. Under these conditions, the lessons from the past remain relevant. The record of these OSS and SOE allies presents a useful, accessible, and detailed case study for how combined UW operations can be done successfully and how to manage relationships among partner nations and mitigate strategic risks. The United States would be wise to invest more thought and study in order to successfully apply history’s lessons. JFQ

Lieutenant Colonel J. Darren Duke, USMC, is G2 for U.S. Marine Corps Forces Special Operations Command, Camp Lejeune. Major Rex L. Phillips, USA, is en route to a tour with Special Operations Command Central, MacDill Air Force Base. Major Christopher J. Conover, USAF, is en route to the Air Staff at the Pentagon and is currently serving as a Joint Branch Chief for the Joint Improvised Explosive Device Defeat Organization.


  1. Nikola Kapetanovic, Tito and the Partisans: What Really Happened in Yugoslavia from 1941 to 1945 (Belgrade: Jugoslovenska Knjiga, 1952), 45–46.
  2. Ibid.
  3. Mark Grdovic, “Developing a Common Understanding of Unconventional Warfare,” Joint Force Quarterly 57 (2nd Quarter 2010), 136–138.
  4. Anthony Cave Brown, The Last Hero (New York: Times Books, 1982), 156.
  5. Ilija Jukic, The Fall of Yugoslavia (New York: Harcourt, Brace, Jovanovich, 1974), 99.
  6. Ibid., 99–100.
  7. Walter R. Roberts, Tito, Mihailovic and the Allies, 1941–1945 (Rahway, NJ: Rutgers University Press, 1973), 28.
  8. M.R.D. Foot, “Obituary: Colonel D.T. Hudson,” The Independent, November 14, 1995, available at <—colonel-d-t-hudson-1581911.html>.
  9. “Off the Page—Fitzroy Maclean,” STV, December 16, 2010, accessed at <>.
  10. Brown, 156–157; Jukic, 45–46; and Jozo Tomasevich, War and Revolution in Yugoslavia, 1941–1945: Occupation and Collaboration (Stanford: Stanford University Press, 2001), 35–36.
  11. Franklin Lindsay, Beacons in the Night (Stanford: Stanford University Press, 1993), 76–87.
  12. Ibid., 149–165.
  13. Ibid., 27.
  14. Roberts, 142–143.
  15. Brown, 453.
  16. Ibid., 457.
  17. Roberts, 142–143.
  18. Brown, 456–457.
  19. Ibid., 663.
  20. Lindsay, 12, 25.