The answer is relatively straight forward. While there may only have been 2 commissioned officers with MD's aboard they would have had a large staff trained to augment them in either mundane tasks or in first aid, or to serve in their place as needed. And while I cannot find the ship's company breakdown for an Impendence class CVL, only 2 doctors sounds very much on the low side. The Essex's with about double the crew size(Between Ships Company and Air Group) would have closer to 8 or so, but im having trouble finding accurate breakdowns. Within the crew the medical department formed the 'H' department with the senior officer the department head and responsible to the CO for both the medical care of the crew and the efficient administration of their offices which included the sick bay with recovery wards, isolation ward, operating and patient rooms, and a pharmacy to disburse treatments, and on larger ships a separate dentists office.

But for ow lets talk about how the crew was organized and what happened when things got hot. The enlisted crew would be made of two groups, men rated as Pharmacist Mates and Hospital Apprentices, these men would range from young newly trained men to old salts with decades of experience and very much able to perform most of the same functions as a doctor when it came to day to day needs, and first aid and treating immediate injuries during battle. After the war these Rates would be combined to the modern version of the Hospital Corpsman Rate.

In battle then there would be several casualty collection points established, usually a forward and aft battle dressing station, and an auxiliary to each, along with a central one at the sickbay. Wounded men would be brought to each and triaged with what care could be provided and ordered in priority for further care or operations as possible or called for.