The main part of my military career was on the Puma HC1, which at the time had a seat which could at best be described as an afterthought. The seat back was too short, so that the shoulder harness attachment point was below the height of your shoulders. Tightening the shoulder straps caused your spine to stoop. Also, the thin seat cushion had collapsed on most aircraft. So for those below a certain sitting height, the only way to see the landing point was to look under the instrument panel, rather than over it! I spent much if my early flights sitting on a map pack! Thankfully, the aircraft only had an endurance of about an hour and a half! The later seat, which had a base consisting of the fibreglass personal survival pack, was a big improvement. A later mod was to fit a raised hoop to the back if the seat to bring the shoulder harness attachment point up to somewhere near shoulder level. Needless to say, my spine is rather messed up.