Other Obstacles

Dragons Teeth and Nets


Other obstacles to hinder barges from landing included off-shore nets and ‘dragons teeth’. Offshore nets were laid by the Royal Navy but were later replaced with tubular beach scaffolding. Dragons teeth were steel spikes set in concrete and laid at the low water mark.  In total 55th Division constructed 6,788 heavy and 4,944 light spikes.  Of these, 558 Field Company certainly constructed the majority - the War Diary notes that 4,427 spikes of 12” by 5” girders set in concrete blocks laid at 15 ft intervals were constructed as well as 1,886 smaller spikes (dimensions not given).  Steel cable was strung between the spikes as well as barbed wire.


Remains of Dragons teeth at Minsmere included 15 teeth still in situ (12 removed in summer 2013 for H&S). These teeth were constructed wit 8” x 4” steel girders; it is uncertain if these were heavy teeth or the lighter teeth.  Two types of teeth were produced, one with a single point made by cutting of the end of the girder at and angle and tapering the top edge to create a spike. The second type is double pointed, with a much longer and narrower spike along the top edge and a more substantial spike on the bottom edge.  The spikes were set in concrete rafts of approx 80” x 60” x 12”. Remains of a fibrous material was in evidence on one of the rafts – perhaps the remains of a jute bag; pouring a semi-dry concrete mix into jute bags is certainly one of the methods used for concreting under water.




















 Above: The single spike type of Dragons tooth, Minsmere

















Above: The double spike type of Dragons tooth, Minsmere





















Above: Left -  'Dragons Teeth' and Z1 Naval Scaffolding remains, post WW2, Minsmere Beach.  Right - sketch of Dragons tooth from remains at Minsmere 2013.


Block Ships


The War Diary of 2/4th South Lancs mentions 'block ships' sunk at the entrance to the Blyth Estuary to prevent enemy ships/barges from entering the Estuary mouth. 'Block ships' were also to be sunk at Downham Bouy, River Orwell and the entrance to Ipswich Docks (46th Brigade Defence Scheme).


Rail Blocks


Railways in places were also to be blocked. Such blocks would consist of a 'fixed portion' at the sides and a 'moveable portion' across the running line. At first the 'moveable portion' consisted of a waggon filled with ballast etc which could be pushed into position and their wheels or axles damaged with explosives. These are often referred to as 'Wagon blocks'. Later on bent rails (as in road blocks) were used for the 'moveable portion'. The 'fixed portion' consisted of concrete cubes.


Floating Mines


Floating mines were to be employed in the River Alde to act as a deterrent to enemy assault crossings or bridging from Orfordness and seaplane landings. Two stations for launcing mines were constructed at Slaughden Quay and Orford Yacht Club, consisting of 25 mines, telephone communications and launching apparatus. They were to be manned by three other ranks on 'Action Stations'.




558 Field Company R.E. papers, TNA

Tubular Scaffolding, WO199/2554, TNA

2/4 South Lancs papers, TNA

46 Brigade papers, TNA

45 Brigade papers, TNA

Field Engineering (All Arms), MTP No 30 Part III Obstacles, The War Office, 1940

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