 The planners then examined whether a commando force was feasible to accomplish the task . An unusually high spring tide was due in March 1942 which would allow a light ship to pass over the sand banks in the estuary and approach the docks , bypassing the heavily defended dredged channel . The approach was too shallow for an infantry landing ship , but the planners believed if a destroyer could be lightened it might have a draft shallow enough to enable it to get through . 
