FOR his final tour of duty in the Transformers director’s chair, Michael Bay doesn’t go out with just one bang, he unleashes a barrage of ground-shaking booms.

Transformers: The Last Knight is the cinematic equivalent of giving a four-year-old a drum kit for Christmas then subjecting us to two-and-a-half hours of the excitable tyke pounding the toms, bass and snare to oblivion.

Apparently, there are more than 10 prequels, sequels and spin-offs featuring the “robots in disguise” in development.

That’s a lot of headache medication.

No one orchestrates apocalyptic destruction with self-indulgent swagger quite like Bay.

For this fifth picture in the series, he takes a thunderous tour down memory lane, incorporating action elements from Armageddon and The Island with a ridiculous origin story tethered to Arthurian legend.

Three scriptwriters overload the picture’s flimsy circuitry with robots great and small including an army of new evil Decepticons - Dreadbot, Mohawk, Nitro Zeus and Onslaught - plus a comical sidekick called Sqweeks fashioned out of spare parts.

It’s impossible to distinguish these mechanised characters in the heat of battle as metal fists pummel metal faces or metal hands tear metal limbs from armatures.

Somewhere in the digitally augmented melee, Sir Anthony Hopkins lazily chews scenery in a thankless supporting role and Mark Wahlberg takes his working class hero to risible new heights as the saviour of the human race.

In 484 AD, King Arthur (Liam Garrigan) leads his knights into battle, flanked by 12 robot warriors summoned by Merlin (Stanley Tucci).

The magician’s staff is buried in time, forgotten until the present day when the revitalised Decepticons, led by Megatron (voiced by Frank Welker), hunt for the precious artefact in order to bring about the end of the world.

Alas, Optimus Prime (Peter Cullen) cannot lead the fight: he is tumbling through space, bound for planet Cybertron and his creator, Quintessa (Gemma Chan).

Thus, fugitive inventor Cade Yeager (Wahlberg) answers the battle cry, aided by a plucky 14-year-old orphan called Izabella (Isabela Moner) and Autobot comrades Bumblebee, Hound (John Goodman) and Drift (Ken Watanabe).

Esteemed historian Sir Edmund Burton (Hopkins), his sociopathic robo-butler Cogman (Jim Carter) and spirited Oxford university professor Viviane Wembly (Laura Haddock) become Yeager’s guides to salvation.

Meanwhile, US Army Lieutenant Colonel William Lennox (Josh Duhamel) and the Transformers Reaction Force led by Santos (Santiago Cabrera) track Yeager’s movements.

Transformers: The Last Knight is unlikely to win new fans to the franchise, hanging spectacular yet soulless special effects-laden calamity on a gossamer thin quest for Merlin’s staff.

Throwaway subplots about parenthood, self-sacrifice and unity are tossed into the melting pot, without any purposeful design.

Bay’s directorial brio elevates the preposterousness to coolly detached watchability.

“Without sacrifice, there can be no victory,” opines King Arthur.

We sacrifice 149 minutes for Bay’s film and there is no sense of triumph.

Just blessed relief when it’s over. 4/10