Posted: 22 September 2010 20:03

Although I covered many of the roadblocks in Rye two years ago, I had yet to visit a sequence of blocks along the Royal Military Road. The most interesting site still has a handful of pimples extant.

I knew of this site already; it is mentioned in the Defence of Britain Project and I had previously stopped at the roadside when I was cycling along the Canal in 2006, but had not got closer. The remains comprise nine pimples, eight of which are still in situ on the canal bank and barely visible from the road.

The photo below shows the lie of the land; on the right the pimples are on the sloping bank of the Royal Military Canal, the Royal Military Road runs alongside, and to the left of the road is a drainage ditch.

Roadblock Recce

Having secured permission from the landowner to climb the gate and walk through the platoon of sheep that were guarding the roadblock, I had my first proper view of the pimples.

They were spaced in rows three feet apart and were dug into the gradient of the bank; I suspect that they survived only because they do not hinder agricultural activity on what is otherwise a narrow strip of land.

Roadblock Recce

The 1941 Roadblock Report gives us an interesting insight into what was originally here: 38 pimples, 20 buoys and four cylinders. Using this data, I attempted to reconstruct the roadblock in its entirety using Google Sketchup.

The landscape

The graphic below shows the basic topography; at left the drainage ditch, the Royal Military Road and then the Canal. The extant pimples on the bank hint that the block was obstructing the ground between the canal and the ditch.

Roadblock Recce

I didn't really measure the ground when I was there; the model is based mostly on my photographs and measurements taken from Google Earth, and admittedly I think the banks in my model are steeper than in reality, but short of a lot of surveying with tape measure and clinometer, the model sufficed for my purposes.

Reconstructing the block

To reconstruct the block, let's start with the eight pimples still in situ; the ninth pimple is a quandary to which we'll return later:

Roadblock Recce

Laying out the pimples

Using the pattern of spacing and alignment we can extrapolate the pattern up to and across the road as seen below. The surviving pimples (marked) provided me with just enough information. They indicate that there were at least five rows of pimples - the number specified by the 1940 Military Training Pamphlet on Obstacles.

We know there were 38 pimples here and the extrapolated pattern gives us enough pimples for some on the far side of the road by the ditch. I must admit not having really looked closely at this ditch during my visit as I assumed that this was sufficient defence without obstacles being built on this side of the road. This is wrong; of course there would need to be pimples here, despite the narrow verge - they would prevent a tank simply nudging the buoys off the road and into the ditch. This sort of thing often only becomes apparent to me when I'm building a model and placing elements in it - this is precisely why I build models! I certainly wouldn't have been able to have extrapolated the pimples when I was actually there having been up close to them for the first time.

Roadblock Recce

Adding the movable obstacles

We know there were 20 buoys and four cylinders at this block in 1941. As cylinders were not really coming into use until 1941, the original block as established in 1940 would have been closed only by buoys. Again, the manual states that buoys are to be deployed five rows deep - therefore, one row of four for each row of pimples as seen below:

Roadblock Recce

How did the cylinders fit in? Speculation leads us to assume that an extra buoy was added to each row and the cylinders put in the middle, although too many obstacles packed too closely together would ironically help a tank defeat the block. We just can't be sure of the arrangement, and the Roadblock Report indicates that no plan of the block had been made.

Roadblock Recce

Something else the report tells us is that this block was not redundant and was to be strengthened. A requirement for a further 14 cylinders and 14 bent rails and sockets was to be submitted; again, whether this actually happened is not known. The graphic below shows the enhanced block. The buoys may or may not have been placed on the road beyond the cylinders; without flanking obstacles on the verge they would have been easily avoided and only of minor nuisance value. The buoys may therefore have been destined for other roadblocks that need additional defences.

Roadblock Recce

The ninth pimple

We've seen the arrangement of the eight pimples that are still in situ; the ninth has been uprooted and only a tree prevents it from rolling into the canal. It currently proves popular amongst the local ovine population as a scratching post.

Roadblock Recce

The 'problem' surrounding this pimple is that it lies a clear 10m away from the others. My reconstruction works perfectly as explained above, but this oddity is confusing. These blocks must weigh a good couple of tons each; how come (if my reconstruction is correct) has this one moved? Removing them must be awkward, hence eight being left in situ.

I can see no benefit of another line of pimples detached from the main group; five rows deep was the prescribed layout of 1940 and the 1941 lists the 38 blocks as the full amount required.

The only observation I can offer is seen below; this pimple (and two of those still in situ) have a small hole cast in opposing faces. These holes are 4cm diameter and 16-20cm deep; they don't actually pass right through the pimple. I've never seen these holes on any other pimples and have no explanation for them other than that they perhaps permitted the pimple to be lifted by mechanical means??

But why would you want to include a method of moving pimples when you construct them? These things were meant to be cast in situ. However, when "in situ" means halfway down a steep bank beside a canal is it easier to precast pimples and lift them into place rather than be running wheelbarrows of cement down a gradient into awkwardly-placed shuttering? Having said this, only two of the eight in-situ pimples also have these holes and the perhaps the 'root' of the pimple looks too rough to have been pre-cast. Some local knowledge may solve this little conundrum; if anyone can provide a clue, please let me know!

Roadblock Recce

I've not mentioned any of the other roadblock sites in the area; these were all within a Home Guard locality with 46 men sharing 26 rifles and four Browning Automatic Rifles between them. The road along this stretch was heavily defended with roadblocks and a complex series of demolitions; of course, the Royal Military Canal was a stop line. It was defended by a line of Type 22 pillboxes, of which none seem to survive in this locality. German intelligence has a few plotted further up the road; aerial photographs may resolve some locations.

This is the first recce I've blogged in some time; I have been out and about and finding a few things that have left me with a grin larger than that I photographed below...

Roadblock Recce

- Pete



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Small concrete roadblock obstacle comprising a truncated cone with domed base. A hollow shaft down the centre allowed the buoy to be manhandled using a crowbar. Buoys were deemed of little value by 1941 and cylinders seen as a better solution.


Reinforced concrete cylindrical obstacles with a shaft down the centre in which could be inserted a crowbar for manhandling, or a picket for barbed wire. Cylinders were 90cm high and 60cm wide and deployed in groups of three as a more effective alternative for buoys.

Defence of Britain Project

A large project run by the Council for British Archaeology (CBA) 1995-2002, collecting data on 20th century military structures submitted by a team of some 600 volunteers. The result was a database of nearly 20,000 records which is available online. The anti-invasion section of the database contains nearly 500 entries for East Sussex.


Term applied to a structure scheduled for demolition or already demolished. Walls and small buildings might be taken down to clear fields of fire or impede enemy passage by destroying a bridge. Some demolitions were not intended to be carried out until after invasion had begun, for example, certain bridges or road craters (pipe mines).


Generic term for a hardened field defensive structure usually constructed from concrete and/or masonry. Pillboxes were built in numerous types and variants depending on location and role.


Small anti-tank block in the form of a truncated pyramid. Pimples were used to extend anti-tank obstacles and roadblocks and were intended for use on soft ground.


Concrete-lined shafts dug into road surfaces into which rails or RSJs (hairpin or straight) could be inserted to form a roadblock. When not in use, a wooden cover was placed over each socket.

Stop line

A physical continuous anti-tank barrier, normally a river and/or railway line, often defended by pillboxes. Stop line crossings (roads, railways and bridges) were to be made impassable.

Type 22 pillbox

A small hexagonal pillbox for six men not commonly seen in East Sussex, though a few still survive along the Royal Military Canal stop line.

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Hibbs, Peter Roadblock Recce (31) - Rye (2019) Available at: Accessed: 21 November 2019

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