At midnight, right on time, 42 Commando Royal Marines in landing craft and US marines in hovercraft hit the dark beach, a few lights picking up the white surf in their wake: "Purple Star" was under way.
The special forces - the American Seals, the British Special Boat Service and the patrol group from 3rd Commando Brigade - were already ashore and 45 Commando had landed by helicopter at an inland drop zone an hour before.
Only the lights told you it was an exercise - if it was real, the ships would have been completely blacked out. But even so, any of the forces invading the fictitious Republic of Kartuna would have heard and sensed the colossal presence just off the coast. Fifty-four thousand British and US troops, sailors and airmen, were driving inland to end the aggression of the neighbouring state of Korona and enforce the UN's will.
They had begun to assemble on Thursday, 30 miles off Onslow Beach, North Carolina. Commanding the assault was HMS Fearless. Ahead was Sir Tristran, repaired after taking a hit in the Falklands, and Sir Galahad built anew after its predecessor was destroyed. On the horizon were eight gunships, sleek shapes like the British Cumberland and Southampton and US warships with 5-inch guns.
As in all military operations the sweat and physical effort at the sharp end contrasted with the almost abstract language and detachment of the planners.
The exercise is part of the final work up for Britain's new permanent joint headquarters, recently inaugurated at Northwood, Middlesex, and of the joint rapid deployment force which includes 3 Commando and 5 Airborne brigades.
In spite of a long tradition of inter-service rivalry in Britain it is clear that in all future operations the services will work together, even at the lowest level. There is still some resistance to the idea, but none was evident "at the sharp end" yesterday.