Service Casualty Branches
The Royal Navy
Given that the Royal Navy has for hundreds of years conducted its business on the High Seas, a unique and unforgiving environment, the disposal of the dead has differed in some significant respects from those which obtained on land. The most obvious difference was the practice of burial at sea, with the dead sailor being sewn into his hammock and committed to The Deep under the White Ensign. The custom of painting the middle and lower decks of warships red in order to render blood less conspicuous, is another interesting aspect of this subject and can be observed in the colour scheme for HMS VICTORY in Portsmouth.
In 1917 the Fundamental Principles of the Imperial War Graves Commission redefined the manner in which burials of the Great War dead were to be handled, for all three Services. The Commission also established the practice of commemorating the fallen on permanent memorials, even if burial took place at sea, or if bodies were not recovered. Another important change was the Commission's rule that no individual could be commemorated on one of their memorials, if their name appeared on a headstone over a grave. The Admiralty belatedly promulgated these changes in 1921. 
Another significant difference was the practice of the Submarine Service of interring crews in mass graves, this practice continued outside the dates of responsibility laid down by the Royal Charter of the Commission. The crews of three submarines managed to avoid the Commission's conventions. Here's how; Submarine E4 sank after a collision with submarine E41 off Harwich, on 15th August 1916, whilst practising runs. The 29 crew were buried in a mass grave in Shotley cemetery. This was long before promulgation of the Commission's regulations, so no problem there. However, the mass grave of the crew of submarine HMS L55 in Haslar Royal Naval Cemetery is another question entirely. L55 was part of the Baltic Battle Squadron engaged in operations in support of the White Russians. Whilst in action against two Bolshevik destroyers on 4th June 1919 she was sunk by a British moored mine.  Bolshevik propaganda insisted that she was sunk by one of their destroyers.  Given the capabilities of the Red Navy at that time, this is unlikely. On 11th August 1928 she was raised by the Soviets. The Admiralty, via the Swedish Government requested that the bodies of the crew be returned. The Soviets insisted that no British warship would be allowed to enter any of their ports. The British merchantman Truro took the 38 coffins on at Kronstadt. They were transferred to HMS CHAMPION at Reval, Estonia on 30th August. As an Estonian Guard of Honour paid honours on the quayside, the coffins were transferred, their band played Nearer My God To Thee. All shipping in the port and government offices lowered their flags. The Guard then fired three volleys and Royal Marine buglers sounded Last Post. The ceremony was completed as HMS CHAMPION left the jetty with her Royal Marine band playing Chopin's Funeral March.  The coffins were buried in a communal grave in the Royal Naval Cemetery Haslar on 7th September 1928. A single large headstone marks their grave. The names of all the crew are inscribed on it. L55 was commissioned into the Soviet Baltic Fleet on 5th October 1921. Nineteen days later she was lost with all hands whilst undergoing trials. She was recovered again and served in the Soviet Baltic Fleet until being scrapped in about 1953. HMS THETIS sank in Liverpool Bay on 1st June 1939, during acceptance trials. Her crew were interred in a mass grave at Maeshyfryd Cemetery, Holyhead. As they had perished before the outbreak of war, they were not covered by the Commission's regulations.