What did flare and hospital drifters do?

What were the roles of flare drifters and hospital drifters or trawlers?

Flare drifters illuminated aircraft or sea targets, while hospital drifters moved casualties as small sea ambulances.

A flare drifter launched illumination for air defense. The same flares could expose sea targets to coastal batteries at night. A hospital drifter or trawler instead moved patients between ships and medical facilities. These small craft effectively served as sea ambulances within a larger naval medical system.