After the outbreak of World War I she was bought by the British Admiralty and converted to serve as a decoy resembling the Royal Navy battlecruiser HMS Tiger.

On 2 March 1903, an article in The Washington Post reported that Merion had run aground shortly after leaving Queenstown while en route to Liverpool from Boston.

The ship was beached below Cross Ledge, but was refloated and made way under her own power back to Philadelphia, after discharging her cargo and passengers.

[1] Merion was employed as part of a program that disguised ocean liners to resemble Royal Navy capital ships.

[1][Note 2] For this duty, the liner was equipped with canvas-and-wood replicas of Tiger's guns, and her crew had to stow them whenever approached by neutral ships.

[8] On 29 May 1915, the German submarine UB-8,[9] apparently tempted by the prospect of sinking a British battlecruiser, allowed five loaded transports to sail past before launching a torpedo attack on Merion.

Some of Merion's crew that were knocked overboard by the explosion were able to float ashore on nearby Strati Island on remnants of the liner's false guns.