world war one a large programme of purchases trawlers to provide
a cheap anti submarine, minesweeping and patrol service. Many
trawlers were purchased and converted During December 1914 to
April 1915, 10 military class 350 tons trawlers were purchased
while on the stocks, and another 9 ex Portuguese were bought the
following September. The Royal navy settled on three standard
designs. these vessels were known as Mersey design. 438 tons,
standard with a full load of 665 tons, the smaller Castle design,
360 tons and 547 tons loaded, and the Strath design 311 tons and
429 tons loaded.
armament were supplied. The Mersey's, Castles and Strath's all
carried one 12- pounder gun, many of them varied slightly by having
the addition of 3.5 to 7.5 inch "bomb Throwers" and
a few had a 4-inch Gun. These trawlers were ordered in three batches
In November 1916 a total of 250. and in 1917 another 150. and
in 1918 a further 140 were ordered.
Blackwater was a Mersey Class trawler, pennant T04, with a displacement
of 438 tons, armed with 2-3 inch guns and carrying a complement
of 20 crew.