Trench Warfare in Korea

7th Infantry Division trenches, July 1953

Fighting with the 2nd Inf. Div. north of the Chongchon River, Sfc. Major Cleveland, weapons squad leader, points out communist-led North Korean position to his machine gun crew. November 20, 1950. Pfc. James Cox. (Army)
NARA FILE #: 111-SC-353469
WAR & CONFLICT BOOK #: 1426

During the Korean War, first in the fighting on the Pusan perimeter from August to September, then, following the Chinese intervention in November, during the bitter fighting of the Battle of the River Imjin in April 1951. Finally, stalemate developed in May 1951 when the UN forces ceased offensive operations just north of the 38th Parallel. Trench warfare subsequently became an unexpected mode of fighting for the next two years. The Chinese mounted several offensives against the UN forces during this period. Battles such as Heartbreak Ridge, which lasted a month from 13 September to 15 October 1951, and Pork Chop Hill, which went on for four times as long from 23 March to 16 July 1953, were not about seizing territory or about defeating UN forces militarily were strategic operations with a political component, designed to influence the negotiations to end the fighting and resolve the question of who controlled Korea. These talks began in July 1951 and continued until 27 July 1953 when a ceasefire came into force. The war has never ended although the ceasefire has been upheld.

After the Communist invasion of the south, the final line of defence was the enforced perimeter around the city of Pusan on the south-eastern corner of the Korean peninsular. Here, the battle for Korea would be won or lost. Everyone, including civilians, was pressed into digging slit trenches and anti-tank obstacles. Whenever the North Koreans came up against the perimeter, which they tended to do piecemeal rather than in a coherent assault, the defenders fought them off in a series of bloody encounters in which the latter were little more than a disparate and ad hoc collection of survivors of the retreat down Korea. Ammunition was short and men tended to drift away from their posts on the defence line, knowing the North Koreans were close. The perimeter was not a continuous line of dug-in troops and armour but rather a series of outposts at strategic points such as road junctions, some little more than a machine-gun and a section of infantry. The key to survival and to defeating the invaders was not allowing these defence islands to dissolve into a general withdrawal when the enemy infiltrated past them, but for the outposts to stand their ground and wait for a counter-attack to deal with the incursion. This was the same principal that had been employed by the Germans on the Western Front from about 1916 onwards and especially in 1917 during the Allied assaults on the Hindenburg Line. The difference in Korea was the heavy presence of reliable and effective tanks on both sides and the considerable air power at the disposal of the UN forces. While the fluid use of reserves to plug gaps, acting as a fire brigade to deal with emergencies, was undoubtedly crucial to the successful defence of the Pusan perimeter, nevertheless, the defence was very much in the spirit of large-scale trench warfare in that it employed similar tactics.

The Battle of the Imjin in April 1951 occurred after the UN forces had mounted an amphibious assault at Inchon and pushed the North Koreans all the way to the border with China. The Chinese intervened and pushed the UN forces back again. During one of the last Chinese offensives before the start of ceasefire talks, the Chinese People’s Liberation Army (PLA) struck hard and without warning at the UN forces north of the 38th Parallel. Some UN troops, such as the British 29th Brigade on the Imjin, became surrounded. A similar situation developed around the Princess Patricia’s Canadian Light Infantry, to the east of the British, who had to be supplied by air drop, a contingency that was first employed in the First World War in 1918. The 29th Brigade, who held the hills through which the River Imjin flowed, were dispersed in strongpoints on hilltops, each separated by a few miles and thus independent of each other but supported by the 25-pounders of 45 Field Regiment, Royal Artillery. Each regimental unit in the Brigade, all of them infantry, held its own hill, the defensive line covering some 7.5 miles. This was a questionable tactical defence, given the fact that the battalion strongpoints could not support each other because they were too far apart. Each position comprised a series of well-dug trenches, foxholes and bunkers, with mortar pits and machine-gun positions sited to give maximum fire support, and arranged by company. While each strongpoint was set out to provide supportive crossfire, the defensive perimeters were open towards the rear and thus vulnerable to encirclement. No barbed wire or anti-personnel mines were available so vigilance was essential and, with that in mind, once contact had been made with PLA soldiers on 22 April, the British had 50 per cent of the Brigade on stand-to during the hours of darkness.

The three divisions of the 63rd Army of the PLA infiltrated across the Imjin and cut between the isolated British strongpoints to attack simultaneously the Northumberland Fusiliers, the Gloucesters and the Belgian infantry battalion that was part of the 29th Brigade during the following night. Initially, the Chinese probed forward with mortar fire but this was merely a preliminary to the infantry assault. Some Chinese even managed to infiltrate among the British trenches in the darkness. Under cover of long-range machine-gun fire, the waves of PLA soldiers crawled to within 10 yards of the British trenches, then threw themselves forward firing submachine-guns and throwing grenades. Wave after wave continued the assault after it became light. Captain Anthony Farrar-Hockley described the fight:

Someone is throwing grenades, and they are throwing them at us. Here comes another one: a small, dark object against the background of blue sky, its wooden handle turning over and over as it begins the descent on to our positions. It falls near Master’s slit-trench; he ducks for a moment as it explodes … Another grenade rises suddenly into the air.

Some Chinese had stayed behind after the last assault on the Gloucesters and concealed themselves behind some felled trees some 15 yards in front of the Gloucesters’ trenches.

Three of us draw the pins from our Mills grenades, three arms draw back for the throw, three arms come up and over. We take cover as the grenades drop to the ground beyond the tree trunk where we suspect the enemy lies.

This exchange of grenades in which one PLA soldier was killed by the grenades and another shot as he tried to break cover took no more than a few minutes. Grenade fighting, bombing as it would have been termed in the First World War, was typical of trench warfare. This also illustrated the relative lethalities of the Chinese and British grenades. The British No. 36 was one of the most lethal grenades ever devised.

While they suffered heavy casualties, the PLA also caused a significant number of losses among the British troops. Eventually, the British were forced back to new positions which, the following night, were attacked in the same way. In the end, the survivors had no choice but to withdraw. Many of the Gloucesters became prisoners because the 1st Battalion had been cut off.

While this battle, one of the best-known engagements of the war, is usually described in terms of a last stand, it was a trench warfare battle in that the Chinese attacked entrenched static positions. The Chinese tactics and their lack of artillery and air support made this an infantry battle. Had the deployment of the four battalions of the 29th Brigade been such that the strongpoints could have provided supportive fire to each other, the Chinese, who were estimated to have lost 10,000 men in the fighting, would have been faced with a much more formidable obstacle. Given the lack of UN air support and heavy artillery available to the 29th Brigade on the Imjin, it would have made sense to have taken more notice of the principals of defence in depth employed on the Western Front in the First World War. As it was, the 29th Brigade was dispersed in a piecemeal fashion, fought hard and lost.

The Battle of Pork Chop Hill, fought two years later under very different circumstances, was a battle in the trench warfare mould. In many respects, it was little different from the smaller offensives that focused on strongpoints on the Western Front in the First World War. There were, in fact, two battles for Pork Chop Hill, fought a few months apart. Pork Chop Hill was an outpost in the Iron Triangle astride the 38th Parallel and part of the defensive line held by UN forces following the cessation of mobile warfare in Korea. Other than the fact that it was an outpost, the US position on Pork Chop Hill had little military significance. Nevertheless, the US troops who seized and occupied the Hill in October 1951 dug trenches and built bunkers on it to turn the position into a strongpoint, purely for defensive reasons. Nothing much happened for the next two years. Then, in March 1953, the Chinese attacked and took the nearby outpost of Old Baldy, which left the US forces on Pork Chop Hill exposed on three sides. Although PLA patrols tested the defences and the resolve of the defenders of Pork Chop Hill each night for the next three weeks, the Chinese did not mount an attack until 16 April when a short but intense artillery bombardment preceded an infantry assault which pushed the Americans off the hill. Some US troops fought on in isolated bunkers but the hill was now in Chinese hands.

With the loss of Pork Chop Hill, the Americans launched an unsuccessful counter-attack on 17 April, followed by a second, this time successful, counterattack the next day, supported by US artillery and mortars which fired approximately 20,000 shells on to the hill. Over the course of two days, US artillery fired 77,000 rounds. The PLA fired a similar number of shells so that Pork Chop Hill was pounded very heavily during the fighting. When the Chinese were dislodged, they mounted counter-attacks to take back what they had lost but failed to push the Americans off this time. The fighting was very much of the type seen on the Western Front in 1917 and 1918, with heavy preparatory bombardments, followed by infiltration into the enemy-held positions. Much of the fighting was hand-to-hand. The occupants of bunkers had to be attacked using techniques similar to those devised during the First World War, modified only insofar as to take into account the greater use of automatic weapons in 1953 compared to 1918. The hand grenade was still one of the essential tools. The US troops had access to what the British had termed SOS fire in the First World War, that is, pre-registered artillery fire to hit their own positions in the event of a break-in, but which had been discontinued by 1918. It had been found to be more likely to cause friendly casualties and waste ammunition than to dislodge the enemy from the position. This was especially true of the fighting on Pork Chop Hill, which was very confused.

The conclusion of this fighting left the US troops in possession and, during May and June, they set about rebuilding and reinforcing the defences. Then, on 6 July, the PLA launched yet another major assault on Pork Chop Hill. Again, the fighting was hand-to-hand trench warfare of the sort typical of the Western Front thirty-five years earlier. To make matters worse, it was the monsoon season and for three days the fighting was in torrential rain. This was a replay of the battle a few months earlier, this time with five battalions of the US 7th Division, instead of a few companies, against two PLA divisions instead one battalion. While the second battle was more intense than the first, it followed a similar pattern to its predecessor, with both sides constantly counter-attacking each other, both sides pounding the hill with artillery and mortar fire, until the commander of the US I Corps decided that enough was enough and withdrew the US companies from Pork Chop Hill, which they left under fire.

If any two battles in any war could be described as pointless, these must surely qualify since Pork Chop Hill had no strategic or tactical significance. However, the ferocity of the fighting and the fact that the UN had not abandoned Pork Chop Hill at the outset, convinced the Chinese that the war and the fighting would continue if a ceasefire was not agreed upon at the talks that were underway at the time of the assaults on Pork Chop Hill. Moreover, a Chinese tactical victory at this stage was politically unacceptable as it would have given the Communists greater bargaining power. In this sense, the battles were far from pointless. Indeed, a ceasefire was agreed within two weeks of the US troops leaving Pork Chop Hill. As was often the case in battles with the Chinese, the casualties were disproportionate. While 243 of the 7th Division were killed in action and another 916 were wounded, the Chinese lost 5,500 men of whom 1,500 were killed in action. The US casualties in April had been about one-third of those in July but the July fighting had gone on for longer and involved many more troops.

Perhaps, the clearest example of trench warfare in Korea was the fighting at the Hook in October and November 1952 and in May 1953. This curving ridge above the River Samichon near the west coast of Korea was part of the static defensive line held by the UN forces since the end of offensive operations in 1951. Like the other posts along this line, the Hook was fortified with trenches and bunkers. It was first occupied by the US 7th Marines who fought off a Chinese assault on 26 October 1952. The Hook was then occupied by the 1st Black Watch of the Commonwealth Division, who reinforced the defences. Barely a month after the first assault, the Chinese launched a second one on 18 November. Again the defenders successfully fought off the Chinese. By the time of the third assault in May 1953, by far the largest battle of the three, the defences had been reinforced further so that the position closely resembled a strongpoint on the Western Front.

A network of trenches followed the contours of the slopes of the ridge, with bunkers, weapon pits and observation posts dotted along their trace, the whole site being arranged for all-round defence. And like many trenches of the First World War, those in the Hook were infested with rats. Underground passageways, like those constructed by the Japanese on Iwo Jima towards the end of the Second World War, connected the trenches below ground, acting in the same capacity as the communication trenches of the First World War. The bunkers were reinforced with concrete lintels, courtesy of the Royal Engineers, to make them bomb-proof. The position was heavily wired and, when the Chinese eventually attacked, many of them were caught in the entanglements, much as soldiers had been caught in the barbed wire in the First World War. Indeed, for the Chinese to reach the British trenches, now manned by 1st Battalion the Duke of Wellington’s Regiment which consisted mostly of National Service conscripts, they had first to cut the wire entanglements. Yet, there was much dead ground below the ridge line due to the many gullies that lay between the spurs of the ridge. It was up these gullies that the Chinese attacked in May 1953.

An important aspect of the defence of the Hook was the defensive fire plan whereby UN artillery would pound the slopes in the event of an attack. At the same time, machine-guns were sited to sweep the slopes with interlocking fire zones, although these could not engage the dead ground. Without artillery support, the Hook would not have been defendable. The effect of artillery and machine-guns on the waves of Chinese was predictable and they suffered very high casualties.

Like so many battles, the third battle of the Hook opened with an intense artillery bombardment by the Chinese which lasted until well into the night. Indeed, so intense was the shelling that many of the forward positions of the Hook were obliterated. The UN guns responded with counter-battery fire and the result was a prolonged and sustained artillery duel. A little before 8.00 pm, the Chinese launched their assault up the gullies and into the first line of trenches, of which little now remained. The whole topography of the landscape was altered by the weight of 10,000 Chinese shells. The survivors of the 1st Battalion fought back but were overwhelmed. The Chinese threw satchel charges into the tunnels and bunkers. Much of the fighting was again hand-to-hand. British reinforcements arrived to hold the Chinese before another wave of assaults was launched.

This time, the Chinese were met with concentrated small-arms and machine-gun fire, as well as mortar fire. UN artillery destroyed a Chinese battalion forming up below the Hook to make another assault. Nevertheless, a third Chinese assault was made from another direction around midnight. This was met with withering fire and, although Chinese troops managed to get in among the British trenches, the Dukes progressed systematically along their trenches bombing the Chinese out. Not since the First World War had bombing been undertaken from trench to trench as it was in the Hook. And once again, the lethal effectiveness of the Mills No. 36 was shown to be superior to the concussive blast grenades favoured by the Chinese. There were instances of Chinese grenades exploding very close to British troops and wounding them, whereas the No. 36 killed under such circumstances because of the large number of lethal fragments it produced on detonation.

What is perhaps surprising is the low level of British casualties given the intensity of the Chinese bombardment and their persistent assaults on the Dukes. While estimates of the number of the Chinese killed and wounded in the course of the third battle suggest that between 1,500 and 2,000 may have died, most of them to the defensive artillery fire of the UN forces, the Dukes and supporting units suffered only twenty-four fatalities, while 105 men were wounded and another twenty were unaccounted for, probably becoming prisoners. Although well-entrenched troops can inflict such casualties on an attacker, the level of Chinese casualties suggests that, apart from a lack of concern for how many men they lost, their tactics were unsuited to assaults on well-defended positions. Indeed, it is tempting to suggest that had they taken the trouble to study the First World War, the evolution of frontal assaults and the role of artillery bombardments, the Chinese would have devised much more effective tactics in Korea. As it was, they neither learned from the past nor from their own experience and continued to make the same mistakes. While their massed-wave tactics could overwhelm less robust troops, and especially troops who had no cover, to apply such tactics in trench warfare was a recipe for failure. And, indeed, none of the Chinese assaults on the UN positions along the defence line across Korea succeeded. Moreover, their own trenches on the other side of no-man’s-land were too shallow and too weak to serve as more than jumping-off points for assaults.

The period of stalemate that lasted from mid-1951 to mid-1953 was marked by Chinese assaults across no-man’s-land on UN positions. The techniques of trench warfare which might have been applied in this phase of the war were not considered by the UN forces, although their defensive strongpoints often reflected the lessons of the First World War. However, tactics of trench fighting at the small-unit level had to be reinvented as they had not been taught for several decades. It is significant, however, that when the Dukes came to fight down their trenches to remove the Chinese from the Hook, they used similar tactics to those taught in 1917. That this was possible shows that the techniques of fighting in the 1950s, while not specifically related to trench warfare, were much more flexible to the specific demands of the situation than had been the tactics of 1914. That the infantry of the 1920s and afterwards were trained in the use of all infantry weapons, from rifle and bayonet to grenade and machine-gun, was down to the experience of the First World War. These factors enabled most UN troops to adapt to the demands of trench fighting, while the Chinese seem to have ignored them and relied solely on firepower and weight of numbers to achieve their aims. When it came to trench warfare, they were not successful.

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