Simon Glancey has submitted the following:
AC1 Walker was killed aboard the troopship R.M.S. Lancastria, which was sunk with huge loss of life when it was bombed off St. Nazaire. The ship was evacuating Allied personnel from France when it was tracked by the Luftwaffe, and it sank with the death toll estimated to be between 3,000 and 5,800.
He is remembered in Westoe on W101.08 page 93
R.M.S. Lancastria
Lancastria Archive
The CWGC entry for Air Craftman 1st Class Walker