Suffolk was within Area IV and V of Nore Command’s Operation Order “P.E” (see Defence of UK- Naval Operation Plans). Nore Command’s instructions in the event of enemy invasion were:
Area VI – Brancaster-Lowestoft: Possible form of attack was an attempt to invade through Norfolk or capture the ports of Yarmouth and Lowestoft.
Ships and vessels on patrol were based at Harwich and Humber. Nore Command’s instructions to Senior Officers at these ports , in the absence of orders from Nore Command, was to decide which vessels they could send in support but to maintain sufficient forces to ensure the safety of both the Harwich and Humber Areas.
All mine-sweepers, Auxiliary Patrol vessels etc in the vicinity of the enemy were to attack his transports. Those not were to maintain their position until ordered to reinforce the vessels engaged.
As Yarmouth may be required for refueling, The Flag-Officer in charge was to arrange for its approaches and anchorage to be swept for mines.
If the attack was south of Lowestoft, reinforcements arriving from the north were to carry the attack southwards of the ships already engaged until contact was made with the Harwich forces.
If the attack was north of Yarmouth reinforcements from the south were to extend the attack north as far as Weybourne Hope and those arriving from the north were to concentrate at Weybourne Hope and then deploy as necessary.
Area V – Sizewell to Brighlingsea: Possible form of attack was an attempt to seize Harwich or a landing on beaches in the vicinity of Aldeburgh.
The whole cruiser and destroyer force on Harwich patrols were to proceed immediately to attack the enemy.
Auxiliary patrols etc in the vicinity of the enemy were to proceed to attack enemy transports. Those not were to maintain their position until ordered to reinforce the vessels engaged.
The Flag-Officer in charge of Harwich was to maintain sufficient patrol vessels for operations within the harbour and mine-sweeping.
Harbour patrol vessels were to spread themselves up the rivers Orwell and Stour to deal with seaplanes or attempts to cross the estuary by land forces. At least one patrol vessel was to be kept in the Quarantine Anchorage to guard against attack on Felixstowe Docks or Landguard Point.
Flag Officer at Yarmouth to send what forces he could spare south towards Orfordness to reinforce Harwich patrol.
Cruisers and destroyers at Sheerness to proceed north to reinforce the Harwich force but until the situation became clear some force was to be held back to reinforce Dover Area if required. Minesweepers, Auxiliary patrol vessels etc also to proceed north to reinforce Harwich force but sufficient retained to ensure the safety of the Sheerness Area.
The Thames Local Defence Flotilla in the Barrow Deep was to proceed north to attack the enemy transports (those in the Edinburgh Channel to remain at their posts).
Above left: Destroyer. Right: Motor launch used for defense of harbours
Arrangements were made with Home Forces to call for naval support. The Defence scheme of 45th Brigade notes the procedure for calls for fire support from naval ships, which would be made by lamp. This Defence scheme also notes that documentation for the recognition of ships was highly secret and kept only at the Coastal Defence batteries. Troops were not to open fire on any vessel unless a clear attempt at landing enemy forces was clearly in place.
Operation Sea Lion, P Fleming, Simon and Schuster, 1957
Military Training Pamphlet No 3, The Defence, W.O., 1943
45 Brigade papers, TNA