R Lee Ermey has reported.

[RAMd®d]

Wikipedia shows he did Apocalypse Now (1979), Up from the Depths (1979), and Purple Hearts (1984). He became a very busy guy after FMJ.

Wiki also says he gave 'one of the rare performances Stanley Kubrick ever allowed to be improvised'. It also mentions his role as technical advisor who became the DI.

I remember him in a few TV roles, and of course FMJ. I didn't know he was in Boys. I may have that in the Drobo. He was uncredited in Apocalypse.