Table:
text: Comus-class corvette
Ships
Ships
Ship Laid_down Builder Engine_builder Launched Completed Disposition Fate
Comus 17 August 1876 John Elder John Elder 3 April 1878 23 October 1879 Struck 1902 Sold for breaking 1904
Curacoa 17 August 1876 John Elder Humphrys, Tennant & Company 18 April 1878 24 February 1880 Seagoing tender Sold for breaking 1904
Champion 17 August 1876 John Elder John Elder 1 July 1878 7 December 1880 Stokers` training ship Sold for breaking 1919
Cleopatra 17 August 1876 John Elder Humphrys, Tennant & Company 1 August 1878 24 August 1880 Training ship; overflow hulk Sold 1931, broken up 1933

Question: When was the Comus class corvette stoker training ship launched?