Never in the history of war had there been anything like the invasion of Normandy - in scope, complexity, or the issue at stake. Millions of men from many nations -land, sea and air forces- were coming by three thousand ships and fleets of airplanes that filled the skies, bringing with them several million tons of equipment. Their route was across the English Channel, their goal to land on the hostile shores of France and put an end to the rule of Adolf Hitler.

The weather in which to carry out this vast undertaking would have to meet certain complicated specifications. Otherwise, the Allied effort might fail. More than any other one factor, the weather held the key to success. For a number of days in advance there would have to be no winds that would raise a heavy, running swell in the Channel. The winds must be no more than nine-to- fourteen miles an hour in the Channel, or nineteen miles an hour outside it in open water.

The planes carrying troops and supplies needed a ceiling of at least 2500 feet and visibility of three miles. For the heavy bombers, the ceiling should be no lower than 11,000 feet, and the sky at least half-free of clouds below 5000 feet. Medium and light bombers called for a ceiling of 4500 feet minimum and visibility of no less than three miles over the target. For the fighter pilots there should be 1000 feet between the clouds and the ground.

Additionally, there was the problem of the paratroops. Twenty miles an hour was the most wind they could land in safely. The gliders, loaded with troops, could handle a thirty-five-mile wind, but no more. Both should have moonlight, twilight, or dawn, so they could see the earth without being seen too well themselves.

Once the crossing to Normandy had started and the landings begun, there could be no change of mind. The massive quantities of things needed to sustain the assaulting forces on the French coast must be kept coming-guns, ammunition, transport, tanks, food, medical supplies-600 to 700 tons a day for each division. At least five days of favorable weather would be needed to make the operation stick.

Moon, tide, and sunrise were right on June 3, 6, and 7, it was seen. "But the selection of the actual day would depend upon weather forecasts," General Dwight D. Eisenhower, the commander of the invasion, wrote in Crusade In Europe, "It none of the three days should prove satisfactory from the standpoint of weather, consequences would ensue that were almost terrifying to contemplate. "Secrecy would be lost. Assault troops would be unloaded and crowded back into assembly areas enclosed in barbed wire, where their original places would already have been taken by those to follow in subsequent waves. Complicated movement tables would be scrapped. Morale would drop. A wait of at least 14 days, possibly 28, would be necessary - a sort of suspended animation involving more than 2,000,000 men!"

So the burden rested on the backs of the weathermen, in particular on Colonels Krick and Holzman. Working with them were four British, two from the Air Ministry and two from the Admiralty; neither pair had much use for the kind of forecasting the Americans were doing. The presiding British forecaster had said scornfully months before, when Krick first came to London, that a five-day forecast was out of the question. His views on long-range forecasting had survived unaffected by Krick's and Holzman's work for the USSTAF bombing campaign in February.

Making matters no easier was the touch-and-go character of the weather over the North Atlantic and Western Europe at the start of June, showing the usual fitfulness of seasonal change from spring to summer. The British, staying with their traditional short- range forecasts, could see nothing ahead to encourage the launching of history's greatest water-borne invasion.

Using analogues (a previous weather sequence that resembles the current weather chart and immediately before it) selected from their archive, Krick and Holzman saw possibilities. They also saw that, in any event, the weather was going to get no better as June grew older. The first days of the month offered "possible" days, those later, when the tide again would be right, "impossible."

As events came down to the wire, with June 4 picked as the first date, June 5 and 6 as alternates, the arguments among the weathermen grew louder. Several times each day they got together by scrambler telephone from their separate stations in what was loosely called a conference, to talk about how things looked for the next five days: winds, clouds, rain, visibility, condition of sea and surf. The consensus-when there was one-was used by the weather briefing officer at General Eisenhower's headquarters in Portsmouth to advise the supreme commander on emerging weather developments. Group-Captain James M. Stagg performed this function.

The wrangling on the phones became so spirited that Krick and Holzman kept a diary on each day's discussion, taking turns dictating what was said. Beginning on June 2, here is something of how it went, told from the secret record:

"At the 0730 Conference, Widewing [code name for USSTAF, Krick's outfit] indicated no change in their forecasts. . . . Admiralty leaned a bit toward the ETA [Air Ministry] picture so Group-Captain Stagg threw out the Widewing version which was optimistic and prepared a summary based largely upon the ETA-Admiralty picture. . . . Dr. Sutcliff [at Allied Fighter Command, an occasional participant in the discussion] indicated that the forecast, as prepared by Group-Captain Stagg, as far as he was concerned, "was not worth a damn. . . ."

Differences did not improve as the day advanced. At five o'clock in the afternoon, a conference was called from Eisenhower's headquarters by Colonel Yates of USSTAF, who had gone to Portsmouth to help Group-Captain Stagg keep Ike informed. As at the earlier confab, "the ETA continued to throw a note of pessimism in the forecast," with Dr. Petterssen saying "the situation was a treacherous one." The Admiralty agreed with the dark view taken by the Air Ministry, as before.

Krick and Hoizman, however, "continued to offer an optimistic picture."

It was the same with Krick and Hoizman at eight o'clock, Hoizman, who led the discussion, said that "every indication corroborated an optimistic viewpoint." Dr. Petterssen, on the other hand, "came on and reiterated his stand that the situation warranted no optimism whatsoever."

The two sides were still at odds with each other next morning at the six o'clock conference. If anything, they seemed to have dug in a little deeper in their respective positions during the night. "Every indication pointed to a very optimistic viewpoint for the entire forecast period," Colonel Holzman emphasized, while Petterssen, for his part, "took an alarmingly pessimistic view, the Air Ministry going along with him. All was gloom."

Krick and Holzman stood fast. At the next conference of the day, a couple of hours later, they "steadfastly maintained their position on the forecast, which continued to develop exactly as anticipated." This upset Colonel Yates, who complained that Krick and Holzman were placing him in an embarrassing light.

At the war room briefing of 4:15 in the afternoon of June 3, Krick presented the forecast for the next five days. It indicated operational weather for both sea and air forces, beginning after the next day. The British saw it exactly the other way around: weather unfit for either plane or ship throughout the same five days.

The reason for Krick and Hoizman's stubborn optimism was a "wedge development" or high-pressure belt over the Atlantic which they expected to reach the British Isles on June 4, pushing a cold front ahead of it into France and bringing clearing weather in its wake. The wedge had not yet shown up on the daily weather charts, however, so Krick and Holzman decided it was useless to argue and accepted the majority opinion.

Also, this brought a fleeting measure of peace to Colonel Yates down at Portsmouth, who had phoned Krick and Holzman that it would make his job a lot easier if they would agree with the others. Yates didn't say so, but the strain had become too much for Group-Captain Stagg, who had collapsed, leaving Yates to carry the whole load. Nor did it help Yates that the Russians were sending Eisenhower cables advising him not to go.

But at the first conference on June 4, at three o'clock in the morning, with the Admiralty now saying that the outlook was even blacker than they at first thought, Krick and Holzman fought for their views.

"Colonel Krick presented in great detail the Widewing viewpoint in order that the reasons for our optimistic position would be made perfectly clear to the other members of the conference," Hoizman wrote in his notes of the meeting. "Our final statement was that we were in fair agreement with the wind forecast for Sunday (the day now begun), but not the cloud forecast for that day, and that beyond Sunday we had no confidence whatever in the conference forecast (which was for all bad weather)."

But it was no use. The conference forecast prevailed, and the invasion of Normandy was canceled for both Sunday and Monday, June 4 and June 5.

So matters stood through the day until the five o'clock discussion in the afternoon. Suddenly the British wavered. The Admiralty now said it favored Krick and Holzman's picture over that of the Air Ministry, which went on seeing the worst, including fog on June 6 over the beaches in Normandy.

When all again talked things over, at three o'clock in the morning of June 5, Dr. Petterssen began to retreat from his position, indicating he was no longer sure of his pessimistic stand. The Admiralty, which had wavered the day before, wavered some more, saying that "developments seemed to be going somewhat better than they had hoped for." Krick and Holzman "continued to reiterate their optimistic picture."

The conference ended, one of them recorded, "with the implication that the operation [invasion] was on."

Indeed, it was. As the attack unfolded on June 6 without interference from the weather, the generals congratulated Colonels Krick and Holzman for sticking with their forecast despite the disagreement of the others. "If the forecast holds up as you have indicated," said General Edward Curtis, General Spaatz' deputy, "it will make history."

There was something else besides Krick and Holzman's unyielding optimism that the weather would hold which helped the great decision along. On Sunday night, June 4, when the final decision had to be made, and unknown to Krick and Holzman, General Spaatz "had called on General Eisenhower. "I think you should go," Spaatz said. "Our guys know what they're talking about."

With grim humor as the invasion rolled on, General Curtis sought out Krick and said, "We'll all be busted to privates if you two guys are wrong."

Not years alone have turned Krick's hair from jet black to snow white.

With a hold on Europe solidly established, General Eisenhower removed the British from all forecasting functions and assigned this responsibility exclusively to the forecasters of the United States Strategic Air Forces. He elevated Krick to chief of his weather information section, in due course stationed at his forward headquarters at Rheims, forecasting for all operations in the re-conquest of the continent.

Air Marshal Tedder of the Royal Air Force, Eisenhower's chief deputy, was briefed daily by Krick and Holzman. He grew so confident of the pair's ability that he telephoned Krick's headquarters for the weather each time he was in England, ready to fly back to France, ignoring the forecasts of his own British Air Ministry weathermen at RAF stations.

Long-range forecasting as developed at the California Institute of Technology brought one other major benefit to the course of the war. The Allies needed to know the earliest possible time when they could cross the Rhine into Germany with the least chance of being cut off from their supplies by the frequent spring flooding of the river from rain and melting snow high in the Alps. The historical record, as established by a group of engineers and flood control experts sent over from the United States, showed that the Rhine could flood any time until May I.

Krick determined that the winter of 1944-45 likely would be very dry and cold for all of northern Europe. The Rhine would almost certainly be safe from any floods. He handed this information to General Eisenhower's G-2 Chief in January. It placed the odds on crossing the Rhine early in the season without danger of flood at about 92 percent.

Plans were speeded up and the crossing of the Rhine started on March 7. Two months later the war suddenly was over-about the time the Allies were supposed to be still poised on the west bank of the Rhine. Thus at least a part of Germany had been saved for occupation by the Western powers rather than the Soviet