Admiral Sir Lewis Bayly, KCB, KCMG, CVO (28 September 1857 – 16 May 1938) was a Royal Navy officer who served during the First World War.

Bayly married in 1892 Yves Henrietta Stella, daughter of Henry Annesley Voysey; there was no issue of the marriage.

In July 1902, Bayly became commanding officer of the protected cruiser HMS Talbot, serving on the China Station.

In December 1914, he was appointed to command the Channel Fleet, flying his flag in the predreadnought battleship HMS Lord Nelson.

After the exercises, the fleet remained at sea for the night on patrol even though German submarine activity had been reported in the area.

With rough sea conditions and the wind increasing, submarine attacks would have been difficult to carry out effectively and so were not thought to be a significant threat.