First things first; it was not a warmongering desire for conflict with Germany. Before both wars, Churchill consistently advocated for peace. However, he had done so through deterrence; si vis pacem, para bellum.

Before the first war, this had taken the form of overwhelming naval superiority (60% more British ships built for every German one), the logic being that if there was no hope of reaching parity, Germany could be persuaded to take up on a mutual ship-building moratorium. Before the second, the same logic was applied, but to military strength as a whole. Unfortunately for Churchill, the interwar period was the golden age of a school of thought that believed the way to eliminate conflict was to eliminate weapons.

Why is this relevant? Well, it informs the total reluctance of the rest of the British establishment to accept what was right in front of their eyes. If they accepted the conclusion Churchill came to, then war was inevitable, German rearmament was not benign, and failing to rearm themselves would not reduce the chance of war. They would have to sell a war mentality, as they saw it, to a British people so avowedly pacifist that the Oxford Union voted 275-152 in February '33 'that this House will in no circumstances fight for King and Country.'

Churchill on the other hand, saw Hitler for what he was, which could be found simply by reading Mein Kampf. Sir Horace Rumbold, Ambassador to Berlin from 1928 to 1933 had done so, and also warned London with similar prescience. They both understood that Hitler was a fanatic.

Many assumed (or were desperate to believe) he was just another version of Wilhelm II. Churchill had met the Kaiser pre-Great War, and had seen fanatics in the Sudan Campaign of the Mahdist War. He had little doubt that Nazism was seeking to overturn all of the world order, not just rectify a punitive peace. Two months before Hitler came to power, Churchill gave the following speech:

Now, the demand is that Germany should be allowed to rearm. Do not delude yourselves. Do not let His Majesty's Government believe, I am sure they do not believe, that all that Germany is asking for is equal status. I believe the refined term now is equal qualitative status, or, as an alternative, equal quantitative status by indefinitely deferred stages. That is not what Germany is seeking. All these bands of sturdy Teutonic youths, marching along the streets and roads of Germany, with the light in their eyes of desire to suffer for their Fatherland, are not looking for status. They are looking for weapons, and, when they have the weapons, believe me they will then ask for the return, the restoration of lost territories and lost colonies, and when that demand is made it cannot fail to shake and possibly shatter to their foundations every one of the countries I have mentioned, and some other countries I have not mentioned.

Until the invasion of Czechoslovakia, the British establishment maintained its refusal to admit this. Every one of Hitler's moves was framed as 'the last act,' and every time the establishment deluded itself into thinking he was speaking the truth, and every time Hitler went back on his word and renewed his aggression.

Bouverie, Tim, Appeasing Hitler: Chamberlain, Churchill and the Road to War, (London, 2019)

Roberts, Andrew, Churchill: Walking with Destiny, (London, 2019)