Who is Corpsman Ken "Doc" Caswell from With the Old Breed, at Peleliu and Okinawa and what is their importance?

Corpsman Ken Caswell is a marine corpsman attached to Sledge's company. Little biographical data is offered on Caswell. Sledge notes that he is fearless, compassionate, and dedicated. On one occasion, Caswell renders first aid to a wounded marine; another marine cuts open medical supplies and accidentally thrusts his knife into Caswell's face. Seriously wounded, Caswell continues performing first aid while Sledge holds a bandage to his face to staunch the bleeding.