HMS Mantis

Sidney Thorne's service record shows him as serving on HMS Alert(Mantis) 
and Dalhousie (Mantis) during WWI.

Alert & Dalhousie were depot ships at Basra at the time of Sidney 
Charles Thorne's service. The gunboat Mantis is the vessel listed in 
the brackets next to them. So he would of served on the Mantis.

Mantis - HMS Mantis was a Insect Class River Gunboat.
   
Launched 14/9/15 and sold in China 20/1/40.
  
645 tons, 230ft long x 36 ft wide and carried 2x6" and 1x3" guns.
  
These insect class gunboats were used extensively on the rivers in what 
was known as Mesopotamia (modern day Iraq).

In 1916 Gnat, Mantis, Moth and Tarantula were towed out to the Persian 
Gulf to join the Tigris Flotilla. Over the next two years they, together 
with the rest of the expeditionary force, fought their way all the way 
to Baghdad.

Bughaila Feb 1917, The Tigris River Flotilla (HMS Mantis, Tarantula, 
Moth, Butterfly,Gadfly and Snakefly) assists in the advance on Baghdad. 
They encounter the Turkish river Navy and sink two of their boats,Basra 
and Pioneer. The Firefly in Turkish service is run aground and recaptured.