The Navy covering force for the American reinforcement and supply convoys was hit hard by Japanese submarines. The carrier _Wasp_ was torpedoed and sunk, the battleship _North Carolina_ (BB 55) was damaged, and the destroyer _O’Brien_ (DD 415) was hit so badly it broke up and sank on its way to drydock. The Navy had accomplished its mission, the 7th Marines had landed, but at a terrible cost. About the only good result of the devastating Japanese torpedo attacks was that the _Wasp_’s surviving aircraft joined Cactus Air Force, as the planes of the _Saratoga_ and _Enterprise_ had done when their carriers required combat repairs. Now, the _Hornet_ (CV 8) was the only whole fleet carrier left in the South Pacific.
As the ships that brought the 7th Marines withdrew, they took with them the survivors of the 1st Parachute Battalion and sick bays full of badly wounded men. General Vandegrift now had 10 infantry battalions, one understrength raider battalion, and five artillery battalions ashore; the 3d Battalion, 2d Marines, had come over from Tulagi also. He reorganized the defensive perimeter into 10 sectors for better control, giving the engineer, pioneer, and amphibian tractor battalions sectors along the beach. Infantry battalions manned the other sectors, including the inland perimeter in the jungle. Each infantry regiment had two battalions on line and one in reserve. Vandegrift also had the use of a select group of infantrymen who were training to be scouts and snipers under the leadership of Colonel William J. “Wild Bill” Whaling, an experienced jungle hand, marksman, and hunter, whom he had appointed to run a school to sharpen the division’s fighting skills. As men finished their training under Whaling and went back to their outfits, others took their place and the Whaling group was available to scout and spearhead operations.
Vandegrift now had enough men ashore on Guadalcanal, 19,200, to expand his defensive scheme. He decided to seize a forward position along the east bank of the Matanikau River, in effect strongly outposting his west flank defenses against the probability of strong enemy attacks from the area where most Japanese troops were landing. First, however, he was going to test the Japanese reaction with a strong probing force.