Design details were left to the individual builders, as was Royal Navy practice at the time for destroyers. As a result, no two were alike and there was considerable heterogeneity of detail and appearance, Most noticeably the number of funnels varied from three, in "Cossack" and "Ghurka", to six in "Viking"; the latter, with two single and two pairs of funnels becoming the only six-funneled destroyer ever built. With a light mainmast aft, they were the first British destroyers to have two masts.