He had a cogent point. We have to be careful to strike the right balance with military spending and acquisition programs.
When looking at acquisition programs for complex things like submarines or aircraft, you have to strike the appropriate balance in the number and rate that they are acquired. If you don't buy enough or leave too big a gap in purchases, the industry that can supply them will dry up and you will lose decades of institutional knowledge and experience. If this happens, when you need new submarines again in 30 years you'll have to spend a ton of time and money to rebuild the industry before they can even start producing submarines again, then you'll have to deal with all the mistakes and defects that happen as a result of inexperience.
On the other hand, you don't want to buy to buy 15,000 tanks that will never be used just to keep a senator with a tank factory in his district happy with low unemployment rates. Resources allocated to the military above and beyond what is really required are detrimental because those are resources that can't be used more efficiently on domestic programs that will provide more benefit to the nation.
So you have to strike the right balance of buying enough tanks that the factory stays in the tank making business instead of switching to tractors, but without buying so many that you don't know what to do with them. You'll see several tricks to try to accomplish this balance, such as buying submarines at a rate of 2 per year for the next 20 years. We might really prefer to buy 40 submarines over the next 5 years and then not buy them again for a few decades but that would force the only shipyards capable of producing them to move on to making other things instead.
It is wasteful to buy equipment this way, but less so than rebuilding industry every few decades. It also provides insurance against quickly deteriorating political situations. If you suddenly need as many submarines as you can build and as quickly as possible due to a war, it's far easier to expand existing production facilities with experienced personnel that can train new hires.