> Uncle Sam will provide at cost (or for free)
Why should the US pay for England’s problem?
Why should England provide airbases and army bases for US forces (where US law over-rides UK law) at minimal to no cost?
Favors work both ways. We’d not be giving you the subs or missiles, just borrowing a couple of slips and some accommodations until we can upgrade a port (probably Barrow, it already handles subs) to cope with the Trident systems.
The same reason we got involved in WWI and WWII. Because it's Mother England. It's the reason ABCA Armies is a much closer relationship than NATO or any other alliance we've got. Blood is thicker than water. Obviously the blood aspect is a little more dilute than it used to be, but we are ultimately Albion's seed - if not by blood, then by language, law and custom, among other things. The Brits paid for their own deployment in Afghanistan and Iraq, and they paid back all of the Lend Lease Aid we lent to them, in contrast to most of Europe, whose debts had to be forgiven. To the extent we have any friends on this planet, the Brits, the Canadians, the Australians and the New Zealanders are it. And it's because of a common heritage.
Apart from ties of blood and sentiment, it makes sense to court England, if only to pry it away from the European Union. The country is in the midst of a bitter divorce. Why not invite it to an all-expenses paid hunting trip (i.e. provide submarine basing gratis), if only to take its mind off its troubles?