 In war, these forces would collaborate with the three battlecruisers by occupying convoy screens while U-boats and one or more of the O class took out the cargo-carrying merchant ships.The presence of the battlecruisers operating at large would have the secondary effect of forcing the Royal Navy to deploy battleships as convoy escorts, thus weakening any fleet that could engage the Plan Z task forces.As part of the plan, design work on the P class was halted in mid-1939 in favor of the O class.