On the question of cost, the chart on page 5 of that briefing paper is quite an eye opener. It shows that in real terms, after removing the effects of normal inflation, defence spending in 2016-17 was broadly the same as it was in around 1990. Yet the difference in what that "buys" in terms of numbers of aircraft, ships, submarines and people is of a different order of magnitude. OK today's kit is far more high tech, but even so...