what would have happened if the imperial japanese navy had won the battle of Iron Sound near Guadalcanal in 1942? could the japanese forces have seized the islands and the precious airfield?
Easily!
After sinking the CAs, Adm. Mikawa proceeds. He sinks USS San Juan and HMS Hobart, too, bombards the airfield and sinks the 15 transports.
But retaking Lunga Point requires more. The Japanese need to understand they deal with almost an entire divisions and not a mere raiding force. Thus they do not launch the attack at the Tenaru river, but conserve their strength. They rush in 15cm guns to shell the airfield –highly effective in OTL, but too late- and in conjunction with another naval bombardment Cactus Air force is incapacitated for a few days, allowing reinforcements to reach Guadacanal unopposed.
IMO the best POD is the Battle of the Eastern Solomons. Halsey´s careless decision to send Hornet and Enterprise east should have cost him both ships, if luck had not intervened four times in the Americans favour. First a CVL had to abort because of an engine room fire, second two SBDs on recon crippled another CVL with a 500lb bomb and most amazingly one group of torpedo bombers and one group of dive bombers did not score a single hit on USS Enterprise at all. If things had gone normal the USN would have had just one fast carrier –USS Saratoga- for the next half year, while the the Japanese CV-force would have remained largely intact. If Yamamoto had take the opportunity to let his battleship force off the leach, the Marines on Guadalcanal would have been doomed.
and if so, how long could they hold the islands and how do you think this would effect the length of the war in the pacific.
However, it won´t matter in the long run. If GC is lost all the resources that went inot the Solomons campaing will most likely be poured into New Guinea, which is closer to Rabaul anyway. Construction of Essex-class CV prodeeds as planned, so will the 1943 offensiv in the central pacific.