 The minelaying machinery and mines added approximately 54 tons to the submarine's mass, and also had adverse effects on "M3"s diving ability - the time required to flood the large casing (which held 600 tons of water) meant that it took around 5 minutes to dive in calm weather, and at least 13 minutes in rough weather, and was dangerously slow to catch a trim.Rear Admiral Martin Dunbar-Nasmith, head of the Submarine Service, was of the opinion in May 1930, that "...at present "M3" is not efficient or reliable as a submarine and could not with safety be used in war".