There is another important but even less easily discussed than inflation aspect: the nature of the
defence industry, itself.
Fifty to 75 years ago the defence industry was robustly competitive and, consequently, prices, including R&D costs, were (relatively) low. Consider, just as one example, in the high cost aerospace field the fate of
North American Aviation: it was founded in 1928 but only became a manufacturing company in 1934; it designed, developed and produced, amongst other things, the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service Module, the second stage of the Saturn V rocket, the Space Shuttle orbiter and the B-1 Lancer.
P51 Mustang through F86 Sabre to B1 Lancer
But that did not keep
North American from being swallowed up by Rockwell which was, in its turn, swallowed by Boeing. The chain of mergers resulted, in some respects, from qualitatively better aircraft: consider, just for example, the performance envelopes
and the Reliability-Availability-Maintainability data for the North American F86 versus the McDonnell Douglas* F18
Hornet, both flown by the RCAF. We used to have 12 F86 fighter squadrons operating from four flying stations in Europe (Baden-Soellingen, Grostenquin, Lahr and Marville) we replaced them, eventually, with three squadrons on one base. Why? Were the new airplanes more expensive? Yes, that's one part of the answer, but the new aircraft were, also, much, Much more capable - they could fly farther, faster, more regularly (because they were more reliable) and they could do much more once in their target areas. We could, and did, "do more with less." But the development and production costs of the new aircraft were, at least an order of magnitude higher, even allowing for inflation, so going from 300 to 36 aircraft did
not consume a lesser
slice of the defence budget.
Similar things happened to ship building, engine technology, guided weapons, radios, radars and electronics and so on. Performance improved, continuously and measurably, but costs, especially development costs, escalated at even greater rates and the
consolidation of the defence industrial base, throughout the US led West, meant that there was less competition, with the expected consequences. "Competition" in aerospace, for example, now occurs almost only when a Western government of group of government have a
design competition, essentially a set of unprovable promises about engineering and finance, and then
direct a contract to the winner ... cost containment is, in practice, impossible.
(I can recall when the CDS of the day, Gen Jacques Dextraze, went to "war" against
Mil Specs because he was persuaded that they were overly restrictive - making real market competition even more difficult - and precluding "good enough" products. The result was the CUCV, the Commercial Utility Cargo Vehicle, the 5/4 ton truck in the CF, which ended up not saving a whole lot of money because it required extensive adaptation (a 12V to 24V conversion, as one example, a completely new electrical suppression system retrofit as another) before it could enter full service. Gen Dextraze's original idea ~ "why can't those big, tough, all weather logging trucks work in the military?" ~ never got properly answered, but it made us nervous about adapting commercial systems, except, perhaps, in ships where the MCDVs have demonstrated their fully adequate sea keeping capabilities.)
There have been at least a few PhD dissertations on this topic, but there are, also, other problems, including corruption and bad management ... consider, just for example, Prince Bernhard of the Netherlands and the Lockheed bribery scandals and the whole 'business' of regional industrial benefits in Canada. The defence industry has, traditionally, been complicit in projects that add new costs to their products, costs which the corporate shareholders are (properly) unwilling to bear and which must, therefore, be borne, eventually, by the customer ~ taxpayers in America, Britain, Canada and so on ~ through higher prices.
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* Also swallowed up by Boeing.
Edit: typo