This is the first of a pair of photos of a torpedo being lowered into the water from HM Submarine L20. It is from the 1926-1928 album of William Richmond Fell who commanded HM Submarine L3, also of the 4th Submarine Flotilla. I presume the photo dates from 1928.
For comparison, here is a torpedo ("fish") being brought on board another submarine.
Date picture taken
1928 (year is approximate)