During the Great War, Sir Arthur Balfour, the First Lord of the Admiralty, gave permission for Wyllie to cruise in Royal Navy ships, and in the North Sea, Harwich, Rosyth, Cromarty, and Scapa Flow, he made hundreds of studies.
Wyllie witnessed the German Fleet surrender in the Forth and went with the last convoy of battleships to Scapa Flow.
As well as this large oil painting a number of etchings and drypoints resulted from all these cruises. Although not an official war artist during World War I, Wyllie had access to many naval bases and contributed to two books. They were the 'Sea Fights of the Great War: Naval incidents during the first nine months', 1918 and 1919.
During the mid-1870s Wyllie travelled the length and breadth of the Thames and Medway on a barge, converted into a floating studio, filling sketch books and painting evocative scenes of the naval and merchant shipping. He was elected ARA in 1889, following an exhibition of watercolours at the Fine Art Society.
Wyllie's output was prolific, covering all kinds of maritime subjects but with a great interest in the Royal Navy and historic occasions.
Above all Trafalgar caught his imagination and shortly before his death he began work on a huge panoramic painting of the Battle of Trafalgar. The painting took 13 months to paint and was unveiled by King George V in 1930 in what is now the Royal Naval Museum.
Wyllie painted almost to the day he died and is buried in Portchester Castle overlooking the Solent.