I am reading the book, To Hell in a Halifax by Herbert Krentz who was a pilot shot down in early 1944 and spent the remainder of WW2 as POW in Stalag IV B where he asked fellow POWs to write about their last mission and how they came to become a POW.
I have a question regarding one of the entries in the book written by a POW.
In the following entry Lionel Stewart begins his account with,
"One of those Coastal Command "walkers.""

Does anyone have any suggestions as to what the the term "Coastal Command "walker"" means?

I have included part of the entry below to give a better idea of the context.
Lionel Stewart, RCAF. Calgary, Alberta, Canada.
Stavanger, Norway: July 16, 1943. Coastal Command / Hampden
"Dear Herb,
One of those Coastal Command "walkers." Flew in torpedo bomber Hampden. Ditched off the coast of Norway south of Stavanger after coastal bombardment. Picked up by Jerry minesweeper, taken to Bergen...
Stew. February 21, 1945"