Further to the minelaying capacity of both sides:
Since just about any vessel could be equipped to lay mines, there was a certain reluctance in the 1930s to spend money on purpose-built minelayers. The Kriegsmarine had none; a class of four fast (28 knots) and heavily armed offensive minelayers of around 6,000t, carrying 400 mines, was planned but annulled on the outbreak of war.
The RN had HMS
Adventure (launched 1924, cruiser-sized at 6,740 tons, 27 knots), and the new
Abdiel class, four of which were launched but not yet completed.
About eight auxiliary minelayers (converted cargo ships, varying from 3,000 to 10,000 GRT, carrying 240-560 mines) were also in service. According to H.T. Lenton,
British and Empire Warships of the Second World War, p. 304: “While it was left to the naval minelayers to undertake lays in enemy waters, mercantile conversions of large mine capacity and radius of action were used for the laying of mine barrages in areas relatively safe from enemy interference. They were only defensively armed with one/two 4in guns, plus lighter AA weapons, and operated under the cover of the main fleets.”
There were a few destroyers fitted for minelaying available; nine V-class destroyers converted to minelayers in WWI were in 1939 still carried on the list as such, with a capacity of 74 H2 mines, but they were never modernised to take standard WWII mines. A number of the more modern G, H and I class destroyers were also modified for ready conversion to minelayers, and could carry about 60 mines (like the German
Zerstörer).
In addition, there were a few small coastal and “controlled” minelayers.
Minelaying by RN coastal forces (minelaying motor launches)did not begin before 1941 it seems.
The Dutch Navy could have contributed the new and relatively powerful Hr. Ms.
Willem van der Zaan (
http://en.wikipedia.org/wiki/HNLMS_Will ... aan_(ML-2) ), plus a few coastal minelayers (
Nautilus, Jan van Brakel, Van Meerlant, employed at boom defence in the Thames estuary and convoy escort at the time it seems).
Info on British minelaying:
http://www.naval-history.net/xGM-Ops-Minelaying.htm