Scapa Flow, the Clyde and Belfast Lough were the three assembly bases for the assault fleet. The curious stood on the shore between Carrickfergus and Whitehead and at Bangor, spellbound at the immensity of an armada they had never seen before and would be unlikely to see again.
Harry Allen, a rating on the cruiser Black Prince, and two mates got 24 hours' leave. They found Belfast packed with military of many nations and not a room anywhere. In desperation, they knocked on the door of Crumlin Road jail to ask for a bed.
They were given a cell with a bed and a blanket each, plus a cup of tea and a cheese sandwich in the morning. When they rejoined the Black Prince, off Bangor, they were told to write last letters home.
At first light on June 3, citizens living along the shore, who had grown accustomed to the ranks of grey smudges on the skyline, found the great fleet no-one would discuss had vanished in the night. It was Saturday and the invasion was on Monday.
But, as the wind rose and the seas raged in the English Channel, it was postponed. On Sunday night, General Dwight Eisenhower, Supreme Commander, banking on a better forecast, finally gave the order: "Tuesday, we go."
By 8am on D-Day, the BBC was quoting the German reports. The first official admission of the invasion by the Allies came at 9-32, when John Snagge, at SHAEF, Allied HQ, read the communiqué on a worldwide hook-up.
In fact the first wave had gone in at 6-30am, sailing beneath a deafening naval barrage in which the cruiser HMS Belfast - built at the Queen's Island ( Belfast )- played a prominent part. For those men and the two waves which came after, D-Day was a foul, valiant, unspeakable exercise in selflessness.
In the sealed encampments in Hampshire, Wiltshire and Sussex, where the assault troops had been confined for the preceding three weeks, except for route marches under Military Police escort, the tension had wound up inexorably.
One day there was an announcement that services would be held that evening. Afterwards clergy advised the men to put any personal effects in a sealed envelope addressed to their next-of-kin. Then they knew.
The timing available to Eisenhower was narrow. He needed calm seas with a rising tide at dawn; but not so full as to conceal the beach obstacles planted by the German commander-in-chief, Marshal Erwin Rommel; and there had to be a moon for the thousand gliders going in during the night.
Sappers of the Antrim Parachute Squadron, Royal Engineers, were dropped just after midnight, in heavy camouflage with painted faces, near Ranville, charged with preparing a landing ground for gliders due at 3.30
For six months, secret patrols had been reconnoitring the beaches, to test the firmness of the sand for Sherman tanks.
Swimming in from midget submarines after dark, naval surveyors and army engineers brought back sand samples, details of water depths and tank traps.
The British actually had a tank which could swim - a converted Sherman. These were to go in with the infantry, but many sank in rough water. The few that made it flabbergasted the German gun crews, transfixed by the spectacle of tanks rising out of the waves.
Altogether 133,000 troops - American, British and Canadian - were landed on D-Day along a front measuring nearly 60 miles.
In the pitching landing craft, many men were seasick. Boats had to be baled using helmets.
