Contributions made by the American OSS?

The OSS was the forerunner of the CIA and NSA. As such, it was pretty important to the US intelligence-gathering program. Its weaknesses were those of any undercover organization -- not only does the right hand not know what the left hand is doing, the two hands aren't even convinced they are connected to the same body. Meaning, the secretiveness of such secret organizations tends to work against itself at times. Lots of times.