NEPTUNE: The Allied Invasion of Europe and the D-Day Landings. By Craig L. Symonds. Oxford. 422 pages. $29.95.

When it comes to the June 6, 1944, D-Day invasion of France, the focus often is on the valiant role played by the Army.

In his excellent new book "Neptune," author Craig Symonds directs the spotlight onto how the U.S. Navy made the invasion possible.

Symonds begins his story with the Japanese attack on Pearl Harbor, using it as a springboard to trace the often-tense debate between American and British leaders over the war's strategy.

From the outset, Army Chief of Staff General George Marshall and senior American military leaders pressed hard for a direct invasion of Europe, arguing that the only way to defeat the Germans was to take the battle directly to them.

"We've got to go Europe and fight," Symonds quotes Dwight Eisenhower as writing in January 1942, "and we've got to quit wasting resources all over the world - and still more - wasting time."

The embattled British, having suffered serious blows at the hands of the Germans, resisted. Prime Minister Winston Churchill, who believed that the Allies needed to secure the seas and the air and as well as build an adequate supply of ships, successfully pushed instead for the invasion of North Africa.

Just as Marshall feared, the long and resource-heavy slog to secure North Africa ultimately pushed back his plan to return to Europe. Not until 1943 did planners begin in earnest the preparations for D-Day.

The codename for the Navy's operation was "Neptune." Symonds chronicles the fascinating logistical requirements to pull off such a complex invasion. The war plan itself ran some 1,100 pages with specific details for every single ship, no easy task considering the assault on France required more than 6,000 vessels.

Symonds likewise charts the massive buildup of 1.5 million American troops in England. To do so, workers transformed the magnificent luxury liners the Queen Mary and Queen Elizabeth into troop transports.

Originally designed to carry 3,000 passengers and crew, the retrofitted liners at full capacity carried as many as 15,000 troops, who slept atop mess tables and even in drained swimming pools.

Symonds concludes the book with a blow-by-blow of the actual invasion, written with a great eye for visual detail, including how the massive guns from the battleship Nevada gave some sailors nosebleeds.

The author of "Lincoln and His Admirals" and "The Battle of Midway," Symonds has produced a terrific account of the heroic role the U.S. Navy played in making the D-Day landings a success.

Reviewer James Scott is the author of "The War Below," "The Attack on the Liberty" and the forthcoming "Target Tokyo." He lives in Mount Pleasant.