Following the failed assault on Port Arthur, the Japanese were forced to lay siege on September 1st. They decided to launch their main assault against the line of forts that were positioned along the East of the city, with the intent of reducing the Russian defences through subterranean attacks, supported by heavy artillery fire and then an assault from a concealed trench. This trench was positioned parallel to the forts and dug around 1000 yards away in positions where the Russian artillery could not engage them. They were dug at depths of at least six feet deep and twelve feet wide. Three lines of forward moving trenches were then dug in a zigzag shape towards the Erhlungshan, Keekwanshan, and Panlungshan forts, at around six feet deep and eight feet wide. In order to conceal the trenches, the zigzag pattern consisted of a diagonal forward moving line, which then took a sharp turn and moved parallel to the fort wall. The trenches continued forward in this pattern and were covered at intervals with wooden planks with soil and grass laying on top. This work was only done at night with the dug soil being carried out in gabions or on stretchers. While the engineers planned their approach carefully, most of the trench’s positions were eventually seen and the Russians sent out saboteurs at night to disrupt the advance.
Once the Japanese soldiers had reached the slopes of the hills, advanced parallel trenches were then dug that spanned across the entire fortified lines of the Eastern front. This final trench line was created with the intention of massing troops closers to the hills for the upcoming uphill assault. While the Japanese soldiers were then in a better position, they were still facing an uphill assault on the fortresses. Tunnelling operations were also commenced against North Tungchikuanshan and Sungshushan. The tunnels advancing against the North Tungchikuanshan, Erhlungshan, and Sungshushan forts all encountered solid rock below ground and moved at a slower pace. The rock was largely quartzite which was full of seams that could be picked at and broken down. The tunnellers were forced to dig with picks and chisels through the ground though and could only move at a rate of thirty to fifty centimetres per day. Due to the solid rock however, the tunnels required no reinforcing and even allowed for light blasts to be used, which the Japanese resorted to in order to speed up their advance. The Erhlungshan tunnels were dug at two feet wide and two feet eight inches tall, which is just enough room for a single person to crawl through and given the fact that the rock was so much work to get through, a smaller tunnel allowed for less work.
The East and West Panlungshan forts were built on softer terrain, a kind of rocky soil that allowed for quicker tunnelling but required fortifications. The softer soil allowed for the tunnels to be dug slightly larger at two feet wide and three feet six inches tall. The tunnels were fortified using timber frames similar to those pointed out in previous chapters and would have been placed regularly to avoid cave ins.
At the Erhlungshan fort, five galleries were tunnelled underneath the front parapet with 5,940 pounds of picric acid placed underneath. At the Sungshushan fort, two tunnels were dug underneath the fort salient, with 14,000 pounds of black powder placed in them. The explosion created from the Sungshushan explosion was huge, leaving a crater about eighty feet wide and 127 feet deep. The scale of the Japanese trench and tunnel network in the area grew vast, allowing them to move within grenade throwing distance of the Russians.
“The total development of siege works as furnished me by an engineer officer of General Nogi's army was' as follows: 13,202 meters parallels, 18,906 meters approaches, 8,352 meters approaches to headquarters, and 682 meters mine galleries, making over 25 miles of siege trenches.”
Impressively, the Ninth Division covered the greatest extent of the operations, creating “5,478 meters parallels, 6,880 meters approaches, 3,552 meters headquarters approaches, and 206 meters mine galleries.”
As seen in Figure 4., the Japanese tunnels were quite short in how far they needed to travel, meaning that while air would have grown stale in the tunnels, it would have remained adequate for the tunnellers to continue with their work. Elaborate ventilation systems such as that seen at the Siege of Petersburg would then not have been of any real concern. East Keekwanshan for example, was dug under using two tunnels that were forty feet long, with both tunnels having four side galleries dug with a mine placed inside each of them.
There are reports of Russian counter-tunnelling operations North Tungchikuanshan and Erhlungshan, but they failed to make any real issues for the Japanese. In the counter-tunnel created in North Tungchikuanshan, the Russians detonated explosives towards the Japanese tunnel, but failed to destroy it and the Japanese tunnellers were quick to make use of the tunnel. At Erhlungshan, the Russians were advancing a counter-tunnel to intercept the Japanese but failed to effectively engage their targets before the Japanese detonated their charges. There were a number of targets hit by the Russians, but they failed to do any serious damage or create any major setbacks for the Japanese operations.
Russian forts and Japanese trench and tunnel positions.
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