Vice Admiral Fletcher, the Operation Watchtower expedition commander and overall commander of Task Force 61, which included the all important aircraft carriers, was operating on Nimitz’ principle of “calculated risk”, “which you shall interpret to mean the avoidance of exposure of your force to attack by superior enemy forces without good prospect of inflicting, as a result of such exposure, greater damage on the enemy”. And Fletcher’s carriers, at the time America’s most precious military capability, were dangerously exposed in the waters off Guadalcanal.
From an intelligence point of view, Operation Watchtower was “a stab in the dark”, and the Allies had no real idea what was waiting for them in the Solomons. If the remaining Japanese carriers were at Rabaul when the landings began, their planes could appear at anytime from any direction beginning on the 9th of August 1942. And it wasn’t like the Saratoga, Wasp, and Enterprise could hide: the Japanese knew exactly where they were.Two weeks previously, off Fiji on the Saratoga at the final commander’s conference prior to Operation Watchtower, Fletcher announced that the carriers would only remain off Guadalcanal until the 9th, and this infuriated both RearAdm Kelly Turner, the commander of the invasion force, and MajGen Vandegrift, the commander of the 1st Marine Division. The gentlemanly southerner Vandegrift almost lost his cool as he calmly explained that they would need more than two days to unload the transports, especially since there were no docks or port facilities available. Everything would have be manhandled over the beaches. Turner, a protege of the gruff Adm King who was no fan of Fletcher, did lose his cool as he complained the Watchtower timeline left him no chance to reconfigure the transports from a commerce load, i.e. packed for efficiency, to a combat load where the critical items e.g. food and ammunition, can be off loaded first. In a conversation in a passageway during a break, Turner was overheard calling his nominal superior “yellow” if the carriers departed before the 11th of August.
But Fletcher had fuel on his mind among many other things. There weren’t enough oil tankers in theater and America couldn’t produce them fast enough. None of the resurrected battlewagons damaged on 7 December were in the South Pacific precisely because they hogged the available fuel. Furthermore the US Navy’s proficiency in underway replenishment was poor at best and operationally detrimental at worst. The Watchtower task forces might as well have been tied to a post like a dog. That post was Noumea, Caledonia, and the chain only extended as far as Guadalcanal, and then only for a few days.
On 8 August, 1942, Fletcher’s carriers had five days of fuel left at cruising speed (15kts) or two at battle speed (25 kts). The fast battleship North Carolina, which was of the newest class and much more fuel efficient that her predecessors, had less than that, due to an unfortunate staff error involving a chart with an incorrect marking for the Intl Date Line, which forced the North Carolina to be late to the rendezvous and unable to top off.
But it wasn’t just fuel, in defending against the Japanese air attacks over the past two days, Fletcher’s carriers had lost nearly 20% of their planes, and they hadn’t even come across any Japanese carrier borne aircraft yet. Fletcher had two carriers sunk from underneath him previously, the Lady Lex in the Coral Sea in May, and the Yorktown at Midway in June. He was tired of getting his feet wet and the losses were fueling rumors that he was senile and incompetent. He wasn’t going to stick around for a third time. He only had two days of fuel for battle then he’d be forced to retire in any case. If the Japanese did show up on the 9th or 10th, he’d rather engage them on the 11th with a full belly. The Japanese carriers weren’t going anywhere once they were off Guadalcanal. This wouldn’t endear him to the Marines taking the brunt of the air attacks, especially after the Navy abandoned Wake Island in similar circumstances earlier in the war. Marines have long memories.
In the end Fletcher’s departure on the 9th was probably for the best. Any Marine casualties on Guadalcanal due to the air attacks would be a tragedy, but a local one. The loss of the carriers would be a national tragedy. In the cold logic of war, there were more Marines in training and in the pipeline to the South Pacific. This was not true for aircraft carriers. The next American carrier scheduled to come out of a shipyard wouldn’t be ready for another six months at best (the USS Essex would be commissioned in December 1942 and then the Bonhomme Richard in April, 43). Until then, Fletcher’s carriers were the only thing standing between Japan and wherever they decided to strike next.
Fletcher made his final decision on the night of the 8th to depart Guadalcanal the next morning, despite vehement protests by Turner and Vandegrift. The transports weren’t even close to being unloaded, though there is some evidence that the unorganized Marines on the beach were just as much to blame. Nevertheless, with heavy carrier fighter losses beating back the numerous Japanese land based planes, low fuel, and his escort ships clearly out fought in night surface actions, Fletcher took his ships, and by default Turner’s, out of the confining straits off of Guadalcanal and into the open ocean where they could be more easily defended and refueled.
The Marines securing the beachhead and airfield on Guadalcanal were on their own.