View source for Sapping

{{Short description|Type of siege operation in warfare}}
{{for|the geomorphic process|groundwater sapping}}
[[Image:Sap Roller.jpg|thumb|325px|Union troops of the [[1st New York Engineers]] digging a sap with a sap roller on [[Morris Island]], 1863]]
 
'''Sapping''' is a term used in [[Siege|siege operations]] to describe the digging of a covered trench (a "sap"<ref>{{Cite OED|sap|id=170794}} (noun)</ref>) to approach a besieged place without danger from the enemy's fire.<ref name=verb>{{Cite OED|sap|id=170797}} (verb)</ref> The purpose of the sap is usually to advance a besieging army's position towards an attacked fortification. It is excavated by specialised military units, whose members are often called [[sapper]]s.

By using the sap, the besiegers could move closer to the walls of a fortress, without exposing the sappers to direct fire from the defending force. To protect the sappers, trenches were usually dug at an angle in zig-zag pattern (to protect against [[enfilade|enfilading]] fire from the defenders), and at the head of the sap a defensive shield made of [[gabions]] (or a [[mantlet]]) could be deployed.

Once the saps were close enough, siege engines or [[cannon]] could be moved through the trenches to get closer to—and enable firing at—the fortification. The goal of firing is to batter a breach in the [[Curtain wall (fortification)|curtain walls]], to allow attacking infantry to get past the walls. Prior to the invention of large pieces of [[siege artillery]], miners could start to tunnel from the head of a sap to [[Mining (military)|undermine]] the walls. A fire or gunpowder would then be used to create a crater into which a section of the fortifications would fall, creating a breach.

Before the development of explosives, sapping was the undermining of an enemy's fortifications, which would collapse when the sap's supports were removed.<ref name=verb/> Later, explosives were placed surreptitiously in the undermining sap or mine, then detonated, as was done with 450 tons of high explosive in the First World War [[Mines in the Battle of Messines (1917)|battle of Messines]], the largest planned explosion until the 1945 [[Trinity (nuclear test)|Trinity atomic bomb test]].

==History==

===Pre-gunpowder===

A way to force entry into a fortified structure was to dig a mine or sap under defensive walls, typically shored up by wooden props. On collapsing the tunnel, for example by burning the props, the wall would collapse.<ref>{{cite web |url=http://news.bbc.co.uk/local/kent/hi/people_and_places/history/newsid_8332000/8332214.stm |title=Ironclad: The siege of Rochester (1215)|website=BBC |date=29 October 2009}}</ref>

===1500s===
Sapping trenches, cannons and gunpowder explosives were a potent force against fortifications. However, the [[Siege of Godesberg (1583)|Siege of Godesberg]] of 1583 during the [[Cologne War]] showed that fortresses could still withstand sapping and explosives to a point. After the attacking force of [[Ferdinand of Bavaria (soldier)|Ferdinand of Bavaria]] fired on the fortress with large caliber cannons; this had little impact on the walls. The cannons were firing heavy shot, but the height of the fortress significantly reduced the force of the impact with the walls, which bounced off to little effect, although the fortress dated from the 14th century. To breach the walls, Ferdinand ordered his soldiers to dig into the feldspar supporting the side of the mountain and place an explosive charge. Even after the powder was ignited and a substantial portion of the wall, the gate, and the inner walls were breached, the defenders still held out for three days.<ref>{{in lang|de}} [[Ernst Weyden]]. Godesberg, das Siebengebirge, und ihre Umgebung. Bonn: T. Habicht Verlag, 1864, p. 43.</ref>

===''Trace Italienne'' forts===
[[File:Fortbourtange.jpg|thumb|325px|The star-shaped [[Fort Bourtange]], restored to its 1750 condition, is an example of a ''trace italienne'' fort.]]
{{Main|Trace Italienne}}
Sapping became necessary as a response to the development and spread of ''trace Italienne'' in defensive architecture in the 1500s. The Italian style star fort bastion made siege warfare and sapping the ''modus operandi'' of military operations in the late medieval and first decades of the early modern period of warfare.<ref>Charles Townshend (editor). ''The Oxford history of modern war''. Oxford: Oxford University Press. 2000, p. 28.</ref> Fortresses with abutments with gentler angles were difficult to breach; cannonballs and mortar shells often had little impact on the walls, or impact that could be readily repaired after night fell. Towers no longer protruded at right angles from the wall; rather, they blended with the wall. These created a two-fold advantage. First, defenders in the towers had a field of fire of 280 degrees or more. This range of fire and the towers' positioning allowed defenders to fire upon the attackers' flank as they advanced, a deadly fire called [[enfilade]]. Consequently, a hostile force which ranged their cannons was less effective, as the "hostile cannon [had] to fire from longer range" and defenders could better enfilade attackers.<ref>Townshend, pp. 28-29. ("Such projections from the wall both forced the hostile cannon to fire from longer range and enabled the defenders to enfilade attackers.")</ref>

===1600s===
[[File:Clampe's map sap detail.jpg|thumb|A detail from the Clampe's map of the siege of [[Newark-on-Trent|Newark]] (6 March 1645 – 8 May 1646) showing in green a sap that allows Roundhead siege artillery to be placed closer to the fortifications of Newark than the circumvallation. Notice that the lines of advance of the zig-zag are at such an angle and position that the defenders were unable to bring enfilade fire to bear.]]

During the English Civil War, there was a siege of [[Newark-on-Trent]] which took place from 6 March 1645 – 8 May 1646. A detailed map of the [[Cavalier]]s defences of Newark and the lines of [[circumvallation]] and [[contravallation]] along with the besiegers redoubts and fortified camps was drawn up by R Clampe, the besieging [[Roundhead]]s' chief engineer. It includes a zig-zag sap emerging from a bastion of the circumvallation. The zig-zags are at such angles and positions that the defenders were unable to bring enfilade fire to bear. Once the sap was completed four cannons were placed much closer to a gateway than those in bastions of the circumvallation.

===American Civil War===
In the [[American Civil War]], troops advanced their sap under cover of a sap roller<ref>{{Cite web | title=CWFF Website: Dictionary of Fortification: Sap Roller | url=http://civilwarfortifications.com/dictionary/xgs-003.html | archive-url=https://web.archive.org/web/20030512052421/http://www.civilwarfortifications.com:80/dictionary/xgs-003.html | access-date=2025-01-16 | archive-date=2003-05-12}}</ref> or mantlet<ref>{{Cite web | title=CWFF Website: Dictionary of Fortification: Mantlet | url=http://civilwarfortifications.com/dictionary/xgm-003.html | archive-url=https://web.archive.org/web/20030509094651/http://www.civilwarfortifications.com:80/dictionary/xgm-003.html | access-date=2025-01-16 | archive-date=2003-05-09}}</ref> by forming a parapet on the engaged side of the trench one [[gabion]] at a time and filling it with earth taken from the trench.

===First World War===

During First World War trench warfare, the combatant's sappers, who were often experienced civilian miners who had been rejected for combat duties due to age or ill-health, strived to undermine each other's positions, working silently to avoid detection. After completing a mine it was filled with explosives, sometimes hundreds of tons, and detonated, followed by an attack on the surprised  survivors from the destroyed position.<ref>{{cite web |url=https://www.bbc.co.uk/guides/zggykqt |title=Was the tunnellers' secret war the most barbaric of WW1? |website=BBC |access-date= 22 April 2019}}</ref>

====Russian sap====
A ''Russian sap'' is a tunnel dug at a shallow depth under [[no man's land]] towards an enemy position. It allows the attacking infantry to approach an enemy position without being detected and safe from enemy fire. For the attack, the tunnel is opened and the infantry attacks the enemy position at comparatively short range. Russian saps were widely used in the [[First World War]], for example during the [[Battle of the Somme]], when four of them were further equipped with [[Livens Large Gallery Flame Projector]]s. Similar tactics were used in the [[Korean War]] by the Chinese [[People's Volunteer Army]], when they dug under the [[Yalu River]] to attack US troops, and by [[Hamas]], when carrying out [[Palestinian tunnel warfare in the Gaza Strip|tunnel warfare from the Gaza Strip]] against [[Israel]].

==See also==
*[[Mining (military)]]

==References==
;Notes
{{Reflist}}

;Bibliography
*{{cite book
 |last=Campell
 |first=E.S.N
 |title=A Dictionary Of The Military Science:Containing an Explanation Of The Principal Terms Used In Mathematics, Artillery, and Fortification, And Comprising The Substance Of The Latest Regulations On Courts Martial, Pay, Pension, Allowances, Etc. A Comparative Table Of Ancient And Modern Geography; Achievements Of The British Army; With An Address to Gentlemen Entering The Army.
 |url=http://civilwarfortifications.com/library/campbell/index-frame.html
 |access-date=2007-11-19
 |edition=New
 |year=1844
 |publisher=James Maynard
 |location=London
 }}
*{{cite book
 |editor=Charles, Townshend
 |title=The Oxford history of modern war
 |year=2000
 |publisher=Oxford University Press
 |location=Oxford
 |url=https://www.cia.gov/library/abbottabad-compound/4F/4FE6BEDB616C0FD2603CA0D307DEE670_MODERN_WAR.pdf
 }}
*{{cite book
 |last=Weyden
 |first= Ernst
 |title=Godesberg, das Siebengebirge, und ihre Umgebung
 |year=1864
 |publisher=T. Habicht Verlag
 |location=Bonn
 |language=de}}

==External links==
* [http://www.civilwarfortifications.com/ The Civil War Field Fortifications Website]

{{Man-made and man-related Subterranea}}

[[Category:Military engineering]]