In December 1915 Mallory joined the Royal Garrison Artillery as 2nd lieutenant and in 1916 participated in the shelling of the Somme , under the command of Major Gwilym Lloyd George , who was son of then Prime Minister David Lloyd George . In December 1915 Mallory joined the Royal Garrison Artillery as 2nd lieutenant and in 1916 participated in the shelling of the Somme , under the command of Major Gwilym Lloyd George , the son of then Prime Minister David Lloyd George .