Ten days after the attack on Pearl Harbor by Japan in 1941, Chester W. Nimitz took command of a shattered U.S. fleet in the Pacific. Four years later, his ships were bombarding the shore installations of Tokyo Bay and his carrier planes were striking at major Japanese cities.

At the time Japan surrendered in August 1945, Nimitz had under his command the mightiest armada under one flag in the world's history, consisting of more than 6,250 ships and submarines and some 15,000 combat aircraft. In addition to 2 million personnel to operate this great force, he had under his command six divisions of Marines. It was a force responsible for sinking 80 percent of the major Japanese naval vessels lost during the war and for the loss of 85 percent of Japan's merchant shipping.

Today is the 100th anniversary of his birth, and a new 50-cent regular issue depicts him in the uniform of a fleet admiral, the highest rank in the Navy, which he attained in 1944. It is the 18th in the Great Americans Series. Since new stamps are almost never put out on a Sunday, the first-day-of-issue ceremony was held two days ago, at Fredericksburg, Tex., his birthplace.

He was appointed at the age of 15 to the Naval Academy, his second choice, because there were no vacancies for West Point, and commissioned an ensign in 1907 after the two years at sea then required. Much of his early sea duty was on submarines at a time when "undersea craft were regarded as a cross between a Jules Verne fantasy and a whale." For more than three decades, he served on submarine flotillas and warships and shore posts, moving up the ladder to rear admiral.

After the Japanese attack on Pearl Harbor left the Navy struggling to recover from the sinking or disabling of eight battleships, he was named to command the Pacific Fleet. He was faced with a twofold task: to rebuild his crippled force and to stem the enemy tide.

In May 1942 came the battle of the Coral Sea in which Nimitz's carrier forces beat off an enemy fleet aimed at enveloping Australia. It was the first sea battle in history in which the opposing fleets never saw each other or exchanged a shot at each other.

Even as that battle was in progress, the Japanese were preparing to challenge U.S. power in the Central Pacific by seizing Midway. Their plans were known in full detail to the Americans, who had just succeeded in solving the Japanese cipher code. To meet the threat, Nimitz mustered every naval unit in the area.

Early in June 1942, a big enemy attack force was sighted, and the three-day battle of Midway ensued. The way Nimitz positioned his carriers was a key factor in enabling U.S. bombers to sink four enemy carriers and damage almost all enemy ships, and inflict the first decisive defeat suffered by the Japanese navy in 350 years.

The Nimitz stamp has been produced in brown by intaglio in post office panes of 100, with a single-digit plate number.

Collectors of first-day-of-issue cancellations have the regular 30-day grace period for ordering -- orders must be postmarked no later than March 24 -- and the customary alternative ways of ordering.

Collectors acquiring stamps: Those buying and affixing stamps on their envelopes, which must be addressed, should send the covers to Customer Envelopes, Postmaster, Fredericksburg, Tex. 78624-9991. No remittance is required.

Postal Service affixing stamps: Collectors affixing stamps themselves on their envelopes, which must bear addresses, should send them to Admiral Nimitz Stamp, Postmaster, Fredericksburg, Tex. 78624-9992. The cost is 50 cents for each stamp affixed on a cover. Payment by personal check is accepted, cash or payment by postage stamps is not.

The following dates, in italics, are the first days scheduled in March for issues from the United States, the United Nations and Canada.

United States -- 5: Mary McLeod Bethune 22-cent Black Heritage USA commemorative, Washington, D.C. 20066; 6: Denominated 14-cent Carroll postal card, Annapolis, Md. 21401; 20: Grenville Clark 39-cent regular issue, Hanover, N.H. 03755; 21: Sinclair Lewis 14-cent regular issue, Sauk Centre, Minn. 56378; 22: Duck Decoys block of four 22-cent commemoratives, Shelburne, Vt.; 23: Ice Boat 14-cent coil, Rochester, N.Y. 14692; 25: Winter Special Olympics 22-cent commemorative, Park City, Utah 84060; 27: Flag Over Capitol 22-cent vending machine booklets, Waubeka, Wis. 53021 and Flag Over Capitol 22-cent definitive and coil, Washington, D.C. 20066.

United Nations -- 15: Four commemoratives for U.N. University in Japan. Canada -- 15: 32-cent space commemorative. CAPTION: Illustration, Chester W. Ninitz. Copyright (c), U.S. POSTAL SERVICE