The ability to construct quick but effective fortifications in the field has historically fallen to the soldiers of the Royal Engineers. This dirty and backbreaking work may not be precise, but it is based very soundly on experience and scientific experimentation. During the 19th and 20th centuries, as weaponry and warfare evolved at a staggering rate, the data provided to frontline engineers also evolved. I have drawn on an extensive collection of military manuals spanning from 1888 through to the modern day to collate this data and publish it in a single place.
The data is for field fortifications such as trenches, and does not include permanent fortifications such as stone built forts. The majority of data reflects protection against small-arms or rifle fire.
Field Works by Major General C.B. Brackenbury (1888)
Protection in the field against artillery
The following table of data was extracted from the Manual of Elementary Field Engineering and updated for inclusion into the 1888 publication.
|Gun||Concrete Butt||Sand & Clay Butt||Rammed Clay||Extreme Penetration||Advised Parapet Thickness|
|7-inch B.L. rifled gun11863 Newhaven experiments||7ft 9in||12ft 11in||18ft 3in||21ft 11in||25 to 30 feet|
|70-pr B.L. rifled gun21863 Newhaven experiments||6ft 4in||14ft 3in||17ft 0in||25 to 30 feet|
|40-pr B.L. rifled gun31863 Newhaven experiments||6ft 1in||11ft 8in||16ft 4in||18 to 25 feet|
|20-pr B.L. rifled gun41863 Newhaven experiments||7ft 0in||10ft 3in||13ft 3in||15 to 18 feet|
|12-pr B.L. rifled gun51863 Newhaven experiments||3ft 2in||4ft 0in||6 to 9 feet|
|10-inch S.B. gun61863 Newhaven experiments||3ft 10in||11ft 0in||12ft 0in||15 to 18 feet|
|8-inch S.B. gun71863 Newhaven experiments||3ft 6in||11ft 5in||12ft 9in||15 to 18 feet|
|68-pr S.B. gun81863 Newhaven experiments||4ft 0in||7ft 6in||14ft 10in||21ft 6in||25 to 30 feet|
|32-pr S.B. gun91863 Newhaven experiments||2ft 8in||5ft 8in||9ft 5in||14ft 0in||18 to 25 feet|
|9-pr M.L. gun101882 Shoeburyness experiments||4ft 0in||9ft (Sand)|
12ft (Medium Soil)
|16-pr M.L. gun111882 Shoeburyness experiments||6ft 0in||9ft (Sand)|
12ft (Medium Soil)
|13-pr M.L. gun121882 Shoeburyness experiments||7ft 0in||9ft (Sand)|
12ft (Medium Soil)
|12-pr B.L. gun131885 Lydd experiments||17ft 0in||9ft (Sand)|
12ft (Medium Soil)
|22-pr B.L. gun141885 Lydd experiments||9ft (Sand)|
12ft (Medium Soil)
Protection against rifle bullets
The following table gives the thickness of material which may be considered proof against rifle bullets of existing service arms (in 1888!) at any range:
|Protective Material||Thickness Required|
|Iron Plate||⅜ inch|
|Steel Plate||¼ inch|
|Fir Logs||12 inches|
|Fir planks, 3-inch thick||6 planks (18 inches)|
|Pack Logs||6 inches|
|Oak planks, 2-inch thick||3 planks (6 inches)|
|Gabions filled with earth||1 gabion|
|Filled sandbags, crossways||2 sandbags|
|Filled sandbags, lengthways||1 sandbag|
|Rope mantlet||6 inches|
|Loose cotton||4 feet|
|Compressed cotton in a bale||2 bales|
The image below from the Imperial War Museum shows a destroyed field fortification from the mid-C19. Experiences such as this would have helped inform measures for ballistic protection. This fort has been constructed primarily using wicker gabions that would have been earth filled. They have also utilised hessian sand bags for additional protection in areas.
Manual of Military Engineering (1901)
The parapet of an infantry trench should be thick enough to keep out a rifle bullet – 2 feet will suffice. Overhead cover was not considered necessary at this time as the enemy’s artillery fire would be frontal, however to protect against oblique fire a thickness of 6 to 9 inches of earth supported by brushwood was advised. The oblique cover was intended to keep out shrapnel, bullets or shell splinters.
Military Engineering, Field Defences (1908)
The following table gives the thickness, in various materials, proof against a bullet from the short Lee-Enfield Service Rifle at 30 yards range. The bullets of some continental armies have, however, greater penetration.
|Clay||5 feet||Varies greatly. This is maximum for greasy clay|
|Earth, free from stones (un-rammed)||3 feet||Ramming earth reduces its resisting power|
|Sand||2ft 6in||Rather more than enough. Very high velocity bullets have less penetration in sand at short than at medium ranges|
|Sand between boards||18 inches|
|Brickwork||9 inches||If well built.|
|Soft wood (fir)||48 inches||24 inch proof at 500 yards|
|Hard wood (oak)||27 inches||15 inch proof at 500 yards|
|Wrought iron, or mild steel||½ inch|
|Hardened steel plate||¼ inch||1/16 inch proof at 600 yards|
|Special hard steel||1/5 inch|
|Coal (steam)||2ft 6in|
|Chalk||1 foot||When freshly excavated|
The 1.457-in Vickers-Maxim gun (pom-pom), which may be taken as an example of light quick-firing gun, fires a 1 lb common shell, with a bursting charge of 340 grains of black powder. Its penetration into wrought iron is 2.25 inches at the muzzle. The bursting charge of the shell is so small that its effect against earthworks is insignificant.
While no data is given for the action of artillery shells, a useful plate was included in this manual showing the effect of anti-infantry artillery shells.
Manual of Field Engineering (1911)
The following table gives the maximum penetration of the pointed bullet in various materials. In order to obtain proof cover, a percentage must be added to these numbers (this number is unspecified in the manual).
|Steel plate, best hard||7/16 inch||At 30 yards normal to plate; 3/16 inches is proof at not less than 600 yards, unless the plate is set at a slope of 3/2 when 3/16 inches is proof at 250 yards.|
|Steel plate, ordinary mild or wrought iron||¾ inch||As above|
|Shingle||6 inches||Not larger than 1in ring gauge|
|Coal, hard||9 inches|
|Brickwork, cement mortar||9 inches||150 rounds concentrated on one spot will breach a 9 inch brick wall at 200 yards|
|Brickwork, lime mortar||14 inches||As above|
|Sand, confined between boards or in sandbags||18 inches||Very high velocity bullets have less penetration in sand at short than at medium ranges|
|Sand, loose||30 inches||As above|
|Hard wood (oak, with grain)||38 inches|
|Earth, free from stones (unrammed)||40 inches||Ramming earth reduces its resisting power|
|Soft wood (fir)||58 inches||Penetration of brickwork and timber is less at short than at medium ranges|
|Clay||60 inches||Varies greatly. This is maximum for greasy clay|
|Dry turf or peat||80 inches|
Tests such as the one below helped to educate and guide the policy on levels of protection required for troops in the field and for equipment being developed for the battlefield. For these, it was essential to have examples of the enemy ammunition and weapons to conduct realistic tests.
Both shrapnel shell and high explosive shell are fired by the field artillery of most foreign nations. Shrapnel with time fuzes can be used up to a range of about 6,000 yards. With percussion fuzes shrapnel can be used effectively against troops behind 14 inch brick or 2 feet thick mud walls as they penetrate before bursting.
Manual of Field Works (All Arms) (1925)
|Material||Penetration||Minimum thickness to be provided||Remarks|
|Steel plate||¾ inches||1 inch|
|Shingle or broken stone||6 inches||9 inches||If pieces do not measure more than 1 inch placed between boards|
|Coal (hard)||9 inches||13 inches||Between boards|
|Coal (kitchen)||15 inches||23 inches||Between boards|
|Brickwork in lime mortar||14 inches||21 inches|
|Chalk||15 inches||22 inches|
|Sand, confined between boards or in sandbags||18 inches||27 inches|
|Sand, loose||30 inches||45 inches|
|Earth, free from stones, unrammed||40 inches||60 inches||Ramming earth reduces its resisting power|
|Sawn timber, hard wood (oak)||38 inches||57 inches|
|Soft wood (fir)||56 inches||84 inches|
|Freshly cut timber logs, 12-in diameter and over||24 inches||36 inches|
|Poles 4.5 to 8 inches in diameter||38 inches||57 inches|
|Clay||60 inches||90 inches||Varies greatly. This is a maximum for greasy clay|
|Dry turf or peat||80 inches||120 inches|
|Snow, rammed||60 inches||Varies greatly. Soft snow has little power of resistance|
Provided that the ground is suitable and that the site is not too close to the enemy, tunnelled dug-outs are the most satisfactory type of shell-proof accommodation on any scale.
Complete protection against shells of large calibre (8-inch and over) can seldom be gained without descending to impracticable depths. The thickness of cover required under these circumstances will be:
|Made earth||35 feet|
|Chalk||25 to 20 feet|
|Hard rock||15 feet|
Royal Engineers Pocket Book (1936)
Protection against the rifle bullet
The data in this publication is the same as the data published in the Manual of Field Works (All Arms) 1925, given above.
The bullets come down at a steep angle and have very little power of penetration. A brick wall 9 inches thick, a bank of earth 18 inches thick or the roof or floor of a good building will be sufficient to stop them.
High Explosive (H.E.) shells with instantaneous fuze
The shells burst directly they touch the ground. The effect is mainly lateral, and is stopped by a 9 inch wall or a bank of earth 2 feet thick.
H.E. shells with non-instantaneous fuzes
These burst after penetrating for some little distance, and are of more value against material than against personnel. The force of the explosive tends to shatter surrounding material. Good protection against the effect of splinters from shells can be afforded by slit trenches.
Little can be done in hasty defences to protect against direct hits of these shells, as the amount of material needed for safety is too great; in deliberate defences, dug-outs can be made deep enough to afford protection.
Field Service Pocket Book, Field Engineering (1944)
The following table shows the thickness of various materials which should be provided to give protection against bursts of 20 rounds armour piercing bullets from LMGs up to 7,92mm or against splinters from 100-lb bombs bursting not less than 30 feet away.
|Earth of loam as in parapets||60 inches|
|Chalk as in parapets||60 inches (variable)|
|Clay as in parapets||72 inches (variable)|
|Sand, loose or between boards||30 inches|
|Brick rubble confined between boards||18 inches|
|Coal between boards||24 inches|
|Road metal 1.5 – 2 inches between boards||14 inches|
|Sandbags, filled with rubble||30 inches|
|Sandbags, filled with earth||30 inches|
|Sandbags, filled with road metal||20 inches|
|Sandbags, filled with shingle||20 inches|
|Sandbags, filled with sand||30 inches|
|Brickwork in lime mortar||18 inches|
|Concrete, unreinforced||12 inches|
|Mild steel plate||1 ¾ inches|
|Timber||60 inches (variable)|
Royal Engineers Pocket Book (1979)
|Material||Bullets||Splinters, shell fragments||Gamma radiation (to at least 75% reduction)|
|Compacted sand (sandbags)||75cm||45cm||45cm|
|Timber||1.5m||20cm (variable)||90cm (variable)|
|Packed and frozen snow||1.2cm|
This information was also replicated in the Commanders Pocket Book, Tactical Aide Memoire 1988.
A good way to represent the advancement of weapons and ammunition is to plot the increase in protective measures required.
|Gravel / shingle||6||6||6|
|Brickwork, lime mortar||9||14||14||18|
|Dry turf, peat||80||80|