The defence secretary’s brain has gone absent without leave. Gavin Williamson said in a speech today that he intends to send his new aircraft carrier, the HMS Queen Elizabeth, round the world to frighten China. He will equip it with a squadron of F-35 fighter jets, purchased from America. In addition he wants to build two British military bases, one in Asia and the other “in the Caribbean”. They are to “strengthen our global presence, enhance our lethality and increase our mass”.

Brexit, says the defence secretary, “has brought us to a great moment in our history”, when we must be ready to deploy “hard power” against those who “flout international law”. What on earth is Williamson talking about – apart from a desire to be Tory leader? His budget was last week said to be £7bn adrift of reality. The Queen Elizabeth cannot sail until 2021. It has no business whatsoever in the South China Sea, where such a vast and unwieldy ship would be a sitting target. The Chinese could sink it in an hour. As for new military bases in the Caribbean and east of Suez, they would cost billions and be an invitation to terrorists. The Chinese must be laughing themselves sick.

Brexit has nothing to do with British foreign or defence policy, since nor did membership of the EU – except that it might involve staying on good trading terms with the Chinese. As for Williamson’s eagerness to go to war against “international law-breakers”, can he not recall the last three times his department tried that, in Afghanistan, Iraq and Libya? They were Britain’s stupidest military fiascos since Gallipoli, if not the hundred years war.

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In his present job, Williamson has a single task. It is to rescue his chaotic budget, laden with the vanity projects of David Cameron and Tony Blair. He should have the guts to cancel the useless Trident missiles and their vulnerable submarines, mothball the carriers and cancel the frigates. They are pure showing off, as pointless as the American jet fighters, almost all of which remain undelivered. Such weapons have no more to do with protecting modern Britain than do muskets, bows and arrows and changing the guard.

Every defence study agrees that Britain primarily needs to be defended from technological and robotic warfare. For soldiers, it needs a core army, trained and equipped for emergency deployment, but nothing beyond what is required by any other European state. As for Williamson’s idea that Britain’s role is to police “Asia and the Caribbean”, has this been cleared with the Americans, let alone the citizens of those countries?

If history teaches us anything, it is that vanity defence procurements merely incite ministers to reckless interventions, afterwards bitterly regretted. Williamson’s speech reads like the pompous rantings of a 1950s Tory on the make. It cannot conceivably have been cleared with colleagues, let alone the Treasury. It is best forgotten.

• Simon Jenkins is a Guardian columnist