Tanks. The clearest example I can give of that Mr Churchill not knowing when to keep his nose out of things that don't concern him. One notable time he would not be told to butt out. They almost certainly would never have arrived in WW1 without him. When would war have ended, 1920, or later? The naval blockade was working, but so very slowly. The Americans, joining in 1917, still duplicated for themselves every mistake of the Allies in 1914 and 1915, except compressed into a far shorter time span. Machine guns without mobility made it inevitable. It needed an idea guy. I hope that doesn't sound too cliched, I'm far from Churchill's biggest apologist.

Churchill adopted tanks as his pet project. As First Lord of the Admiralty, whilst running the Navy, by taking funding from naval things. He formed the Landship Committee, and appointed a naval architect. The Army had thought them pointless. They were initially called land ships because the navy were the only ones who actually did see the point. The Army saw the point after first use. Then wanted lots more of them. The rest, as they say, is history and quite a few tanks have been built since.

Edit: What provokes downvotes here? Surely not for comparing current politicians poorly?

I was just reading how a French inventor offered one of the first submarines in existence as a gift to Napoleon. He refused it.

Imagine if France had instead started massively supporting submarine research and development instead. They could have had a couple of hundred year lead on the rest of the world in submarines and perhaps dominated the seas from then on.

Of course, even then it wouldn't have been so simple, as there'd likely be technology theft and simple inspiration by others that would make their lead not so great. But the potential to make a great difference was there and it was squandered by an otherwise extraordinary leader.

More he was a wartime YC - he backed all sorts of clearly idiotic ideas, and a few of them turned out to be platinum. Would Lord Halifax, Chamberlain or Atlee (or worse May, Johnson or Corbyn) have poured the equivalent of billions into tanks that were crucial in WW1, or into Bletchley that turned out to be the golden goose, or radar? Nope, almost certainly not, they'd have all have died as unproven too, and we'd probably have lost.

An aircraft carrier made of ice is clearly an absurd idea. Yet if it had closed the Atlantic gap, as intended, millions of tons of shipping would have been saved.