You won't find anything at least in western European OSS activities that will match the popular grandeur of intelligence scoops like Midway, but the OSS did have a significant contribution to the war effort throughout the American military's involvement in the Mediterranean theater from 1941-1945. The example I'll provide today is in regard to the American bridgehead at Anzio in Italy. (For another "victory" I would look at Operation Sunrise, the plan to accept the surrender of the German Army in northern Italy headed by Allen Dulles. I've provided sources for further study below) Also, for note, there are several different operational/admin groups within the OSS and the major ones were as follows: Research and Analysis (R&A), Secret Intelligence (SI), Special Operations (SO), Operational Groups (OG), Counter-Intelligence (X-2), and Foreign Nationalities (FNB) all focused on different types of intelligence.

Anzio:

Frenchmen Captain H. E. Andre Bourgoin and Lieutenant John Croze were two of the most successful examples of OSS recruitment of foreign officers to participate in OSS behind-the-line operations. Bourgoin, a French national, had spent the better part of the last twenty-four years managing petroleum concerns in North Africa, and now served as a Mediterranean SO specialist for the OSS. Croze, a former French Army officer, had received a commission into the US Army as a Second Lieutenant. The two men had participated in many different OSS Italy operations, most prominently alongside the OSS in Salerno with Downes later as part of the OSS French desk running operations in southern France from Corsica. Captain Bourgoin brought along Croze to Morocco in early 1943.

Bourgoin and Croze participated in the second wave of the Allied invasion of the Italian mainland in the winter of 1943. While the Allied Armies fought their way up the peninsula, Bourgoin and Croze recruited a group a young Italians who would ultimately render great service to the OSS. The group consisted of Italians either too young to have joined the Italian army or who deserted and wanted to fight on the Allied side. Many Italians had a positive perception of the Allies, especially the Americans, which made it much easier for OSS agents, even Frenchmen like Bourgoin and Croze, to recruit locals for OSS operations.

They recruited approximately sixty Italians from areas in North Africa and Sicily. The two men quickly trained and sent them behind enemy lines in southern Italy on short one to two day intelligence trips to gather vital German Order of Battle information. Their team also collected details on the location of supply and ammunition dumps, gun emplacements, and other high value intelligence. Once the Allies secured Naples and the OSS set up a headquarters on the Italian mainland, OSS MEDTO sent the entire group to training areas where they received further instruction on obtaining accurate information and correct map reading. Captain Bourgoin would later open and command an OSS training area in August 1944, assisting with SO agents.

The group’s greatest achievement came during the Allied Anzio landings in January 1944. With the Anzio beachhead established, the group went ashore with the earliest OSS arrivals. On the beach, Croze remained in constant contact with Sixth Corps headquarters with the assistance of a jeep with a built-in radio transmitter and receiver. Sixth Corps gave Croze daily requests for specific information needed in the conduct of the battle. Croze’s equipment also allowed him to communicate directly with “Station Victoria,” the group of OSS agents stationed in Rome led by Peter Tompkins. Tompkins and his Rome agents worked closely with Croze and furnished timely answers to Sixth Corps’ demands for information. Croze also served as a pipeline for all the useful information at the beachhead coming from the north of Italy to OSS headquarters.

He would eventually relay the beachhead-saving information that originated in Rome regarding an impending German counterattack. During the Allied crisis at the Anzio beachhead, the Rome station provided five reports a day, sometimes an hour in length. Its intelligence came directly from Kesselring's headquarters through an OSS sub-agent who worked on Kesselring's staff. The Rome team, through Croze, warned Sixth Corps’ G-2, Colonel Langeman, of a developing German counter-attack aimed for the sector between the American and British forces. The advance warning allowed the Americans to prepare for the attack and reinforce the British. Langeman credited the information with saving the beachhead.

Sources:

Col. W. A. Eddy and Lt. Col. A. D. Dodds-Parker to Assistant Chief of Staff, G-3, A.F.H.Q., “OSS/SOE Resources for Operations in Italy September – December 1943,” September 18, 1943, Folder 3, Box 39, Entry 99, RG 226, NARA-CP.

Report, “John Croze,” undated, Folder 3, Box 39, Entry 99, RG 226, NARA-CP.

Alessandro Cagiati to Major R. J. Koch, “Forward Echelons,” April 12, 1944, Folder 279, Box 31, Entry 165; Report, “John Croze,” undated, Folder 3, Box 39, Entry 99, RG 226, NARA-CP.

Edward Breed Commander USNR, Attached to HQ, Co. G-2, 5th Army to Colonel Edward J. F. Glavin, “Report on OSS Activities during Invasion of Italian Mainland, September 12 to October 21 inclusive (with recommendations), October 23, 1943, Folder 37, Box 91, Entry 190, NARA-CP, 4-5; Report, “John Croze,” undated, Folder 3, Box 39, Entry 99, RG 226, NARA-CP.

Charles S. Cheston, “OSS Intelligence Teams in Italy,” July 11, 1945, Folder 3, Box 39, Entry 99, RG 226, NARA-CP.

Dulles:

Maj. Judson B. Smith to Commanding Officer, 2677th Regiment OSS (Provisional), “S. O. Branch – Report of Progress 5 December 1944 – 5 March 1945,” March 5, 1945, Folder 8, Box 41, Entry 99, RG 226, NARA-CP.

Neal H. Petersen, From Hitler’s Doorstep (Philadelphia, PA: Penn State Uni. Press)

Michael Salter, Nazi War Crimes: Intelligence Agencies and Selective Legal Accountability (Abington: Routledge-Cavendish, 2007)

Allen Dulles, The Secret Surrender (New York: Harper and Row, 1966)

Bradley F. Smith and Elena Agarossi, Operation Sunrise: The Secret Surrender (NY: Basic Books, 1979).