On 8 December 1941, the United States responded to Japan's treacherous attack on Pearl Harbor by declaring war on Japan.

Senior officers of the United States Navy who were considered to be culpable in relation to the Pearl Harbor disaster were replaced. The Chief of Naval Operations in Washington, Admiral Harold R. Stark, was replaced as most senior uniformed officer in the United States Navy by the energetic, tough and talented Admiral Ernest J. King. Admiral King was appointed to the new position of Commander in Chief US Fleet (COMINCH). Admiral Husband E. Kimmel, who held the position of Commander in Chief Pacific Fleet (CINCPAC) at the time of the attack on Pearl Harbor was replaced by Admiral Chester W. Nimitz in late December 1941.

Admiral Chester W. Nimitz was ordered to halt the Japanese advance across the Pacific, and mount
offensives against them with the warships that had survived the Japanese attack on Pearl Harbor

Admiral King made it very clear that he considered the first priority of the US Navy was to stem the Japanese advance across the Pacific. He ordered Nimitz to defend vital military areas, halt the Japanese advance across the Pacific, protect the sea lanes between the United States and Australia, and mount offensives against the Japanese with the warships that had survived the attack on Pearl Harbor. On 7 December 1942, only three American carriers were in the Pacific: Lexington (CV-2) (also known as "The Lady Lex"), Saratoga (CV-3), and Enterprise (CV-6). Fortunately, the carriers were all absent from Pearl Harbor at the time of the Japanese sneak attack.

Less than a week after Pearl Harbor, Americans received more grim news from the Pacific. Guam had fallen to Japanese invaders on 10 December.

Yorktown returns to the Pacific Fleet

While the carriers Ranger (CV-4), Wasp (CV-7), and the recently commissioned Hornet (CV-8) remained in the Atlantic, Yorktown (CV-5) was ordered back to the Pacific. At the Norfolk Navy yard, her radar detection and recognition capability were improved. Her secondary gun galleries were studded with new 20-millimeter Oerlikon machine guns. On 16 December 1941, Yorktown moved to NOB Norfolk where her air group from NAS Norfolk was hoisted aboard - VB-5, VS-5, VT-5 and VF-42. She also took on board as cargo nine SBDs and twenty F4Fs needed urgently in the Pacific. Yorktown departed Norfolk on the same day for the Pacific.

During Yorktown's transit from the Atlantic, more bad news reached Americans from the Pacific theatre. Wake Island had fallen to Japanese invaders on 23 December after a gallant defence.

Yorktown reached San Diego, California, on 30 December 1941. Two days earlier, she had been designated flagship for Rear Admiral Frank Jack Fletcher's newly formed Task Force [TF-17].

The return of Yorktown from convoy service in the Atlantic was fortunate because Saratoga was hit by a submarine-launched Japanese torpedo south of Hawaii on 11 January 1942 and was unavailable for active service from that date until her return to Pearl Harbour on 6 June 1942. 

Yorktown escorts US Marines to American Samoa

Yorktown's first mission upon her return to the Pacific was to escort a convoy carrying the 2nd Marine Brigade to Pago Pago in American Samoa. The Marines were embarked on the former Matson liners Monterey, Matsonia and Lurline. Departing San Diego on 6 January 1942, Yorktown and her escort warships of Task Force 17 covered the movement of the Marines to Pago Pago where they would augment the garrison already there and build an airstrip at Tutuila.