After the war, DePuy found himself working as an attaché in Hungary, where he stumbled into intelligence:
I did have one experience in Hungary which almost changed the whole pattern of my life. It almost turned me into the intelligence game permanently — something that I did not want. We really were not trained to collect information in a clandestine manner although at the time, Eastern Europe was a boiling pot of clandestine activity. We military chaps were amateurs. But, one day we received a message from Washington to go to Mohacs to report on the Danube bridge which the Germans had dropped in late 1944, as the Russians started their envelopment of Budapest. Some intelligence analyst in Washington was trying to complete the book — there was one being compiled on each country — and there were reports that the bridge was being rebuilt. So, one sunny autumn day in 1949, I put on my Air Force fur collared flight jacket — no hat — civilian trousers and shirt, and stirred up my Hungarian jeep driver — a blond crew cut chap in a field jacket with no hat — and we drove south to Mohacs.
Mohacs, by the way, is the site of the defeat of the Hungarian Army by the Turks. It lies 10 miles or so west of the main highway into Budapest from the southeast, which is the link with Rumania along the north bank of the Danube, and with Belgrade, the capital of Yugoslavia. It is about 75 miles south of Budapest. The trip down was uneventful and the bridge, it turned out, was not being rebuilt. As we returned to the main road leading north to Budapest, we encountered a Russian military convoy proceeding north. It consisted of US jeeps, 2 1 /2-ton trucks, stake and platform 10-ton trucks, plus artillery and towed antitank guns. The convoy seemingly was endless. So, as we sat there at the road junction, we counted the vehicles and recorded bumper numbers. The march units were closed up but there were gaps between serials. After an hour we became impatient and pulled into a gap. The only identification on our jeep was a small 6 by 8 inch enamel US flag on the right base of the windshield. Fortunately, we looked like all of the Russian jeeps in the convoy. Anyway, about 30 miles up the road, the column turned into a huge forested area on the right or east of the highway. A large group of officers and MPs were on the road and there was no way we could avoid turning in so we tucked up close behind a 2 1 /2-ton truck and scooted in with the convoy. The delegation on the road looked at us hard but didn’t stop us.
Inside the forest the road swept around in a large circle. We were moving counterclockwise. To the right, at intervals of perhaps 200 to 300 yards, were parking areas and bivouacs, most of them occupied with Russian troops and equipment. After about a mile, the element we were following turned into one of these areas and we were alone on the circular inner road — and a bit nervous I might add. Soon we came up behind a Budapest municipal water sprinkler wetting down the road. We could see no way out except to follow the circular road. It led us by tank parks, artillery parks, and command posts with lots of radio antennae, etcetera. I kept notes and counted everything. Lo and behold, we finally came back to the point near the main highway where we had entered. The MPs were still there and we chose not to exit through them so we started our second trip around the circuit. After more counting and more nervousness we reached the far side of the circle and found a small firebreak road which we followed to the east. It finally took us out of the forest and we found back roads which led to the main highway north of the Russian encampment.
In the legation I stayed up most of the night preparing a very voluminous and detailed report. In those days we had a book of Russian bumper numbers which identified divisions and regiments. It turned out that we had seen ninety percent of the 17th Guards Mechanized Division moving from the USSR to Hungary in preparation for the invasion of Yugoslavia from the north. In those days we had no satellite photography or other coverage. My report on a scale of A to F for reliability of the source, and 1 to 5 for accuracy of the information, was rated A1 . For a short time I became the darling of the US intelligence community. It nearly did me in professionally. It nearly sucked me into the intelligence business permanently, but after one tour with the Central Intelligence Agency, I was able to squirm out of an assignment to G-2, US Army, Europe (USAREUR), in 1952, and resume my career as a tactical officer with infantry units and staffs.