Lot's of Cold War references here. Elvis Costello was the alpha geek before being a nerd was cool (I was born too early to catch that wave). I'll confess that I didn't catch that Oliver's Army can be a reference to the British Army (as in Oliver Cromwell) until my wife mentioned it to me much later on. At the time it was released I thought that this song referenced mercenaries not the British Army. Apparently Costello meant it to refer to any poor young man given a gun and sent into ugly situations, which could cover either interpretation. It was written after his first visit to Belfast.
The video is from there "Top of the Pops" or Top of the Flops as my dad called it. They are lip-syncing but such is the case with most videos and both the picture quality the syncing here is pretty good compared to some. Plus he's playing a cool hollow body guitar!.