The Boom was a major defensive structure built to stop German submarines entering the major convoy mustering area of the Thames Estuary. The original Boom was built in 1939/40, by sinking wooden piles into the sea bed it was Six miles long when it was first built and stretched from Shoeburyness on the South coast of Essex to the deepwater channels the same was done from the Kent coast at Minster these two piers ran out to the sandbanks a couple of miles off shore, at this point a complex system of gates was laid out.
This saw three ships called lighters weighing 200 tons were anchored in the deep water channel between the two giant piers, suspended between the ships was steel mesh netting, these Boom gates would then open to allow the movement of friendly shipping & convoys. The three lighters the central being the control vessel. Incoming ships sailed between the left and middle ships (
HMS Pallisade was positioned as the right hand ship she was fitted with Horlicken guns; with every 5th shell being a tracer, the same types of guns were fitted to all the Boom defence vessels.
The Boom Defence fleet were also fitted out with ASDIC an early version of what went on to become sonar this was for the purpose of detecting German U-Boats, had one been detected within half a mile of the Boom an alert would have been sent out to a nearby destroyer to depth charge the area. The operation of the gate was a complex affair.
There is a single cable that runs from the "Left" ship around a pulley on a fixed pylon astern of “left” ship this then attaches to the "Mid" ship the boom net is attached to the centre of this cable.
When the incoming ship is cleared to enter the Thames Estuary Control Zone , the left hand moored shop begins to winch in the cable at the same time the mid ship lets the cable run out
This would draw the boom net end towards the pylon and they would then allow the cable to slacken and fall to the seabed. Thus the boom gate would be open for the incoming ship.
The operation is run in reverse to close the gate.
The boom’s construction consists of a double row of posts these stand approximately ten feet above the sea bed and measuring 15ins square. The posts are staggered and stand roughly four feet apart laterally and eight feet apart longitudinally, these are tied together by heavy-gauge angle iron measuring 4.5ins x 5.5ins.
The first section extends East-South-East for one mile before turning to a South-East direction before then turning to a South-South-East direction.
Once the construction of the Boom was completed it took 20 vessels & 400 men to run & maintain the gates, anti-aircraft & anti-shipping batteries by the 532nd Coastal Defence Regiment & the 429 Coast Regiment
The Boom did not ever come under direct enemy fire, in fact the only time it was fired upon was in a friendly fire accident, during April 1941 a practice firing was taking place at the Old Ranges a practice shell failed to detonate at height and fell on to the Boom causing substantial damage to the structure.
At the end of hostilities the ships, gates and anti-submarine nets were quickly removed, the Boom extending out to the deep water from Minster on the Kent side of the Estuary was rapidly removed as it was classed as a hazard to shipping, however a few remnants remain visible on the beach, these being a few of the posts.