The problems that might have been encountered if Arnall’s tunnels had been used are seen in an attack made on 19 December, one of three made on the Helles front to cover the withdrawal at Anzac. The 5th Highland Light Infantry attacked a Turkish trench between the west and east Krithia Nullahs which was overlooked on either side by cliffs about 40ft high. The trench was too heavily defended by a thick expanse of barbed wire to allow attack from the front. During the previous month a tunnel was driven inside the western cliff, through which troops were to emerge on the left flank of the Turkish position. In late November Joseph Murray was sent to complete the delicate work of tunnelling through the cliff:

I have been working to-day in what is known as Beri’s Sap on the left of the Gully. It is a special job and we have been brought into this sector to put the finishing touches to it. Considerable work has already been done; a gallery has been driven down very close to the edge of the Gully and we now have to go forward parallel with the cliffs and keeping as near as possible to them. Measurements have to be taken almost continuously to prevent our breaking through prematurely. We have a long way to go – beyond the Turkish firing and support lines, getting beneath that part of the support line which is in the Gully. The Turkish firing line in the Gully is only a short trench but the redoubt and the mass of barbed wire have made the position unassailable... Some other way has to be found and this is our job. (Able Seaman Joseph Murray, 26 November 1915)²⁴

The intention was to leave just a thin crust of earth, to be broken through immediately before the attack was launched. However, on 10 December, as the miners neared the edge of the cliff, Joseph Murray relates that they miscalculated and suddenly earth gave way to reveal a faint glimmer of daylight. They at once erected a barricade to prevent further falls of earth, but Murray was well aware of the danger of Turkish discovery of the tunnel.²⁵ In fact the premature opening of the tunnel was probably to have serious consequences for the planned attack. By 19 December, Murray recorded that they had nine charges in place, three of which would bring part of the cliff crashing down. The gallery running up to the cliff face had three short branches, which were to be rapidly opened out. The tunnel, however, presented problems. The attackers needed to reach the trench before the Turkish defenders, as a member of the Highland Light Infantry described:

The attack… was obviously handicapped in this race by the fact that it must be initiated from the mouth of a tunnel, entrance to which was difficult and from which it would be necessary to emerge into the nullah man by man. Time was bound to be lost in hastily assembling each party at the mouth of the tunnel and getting it started on its mission, while to rush men forward individually as they left the tunnel would inevitably result in confusion, disorganization and possible disaster.²⁶

The troops were still emerging from the tunnel as the attack was in progress, and those equipped for consolidation with picks and shovels as well as rifles had great difficulty passing along it. Most seriously, the Turks appear to have detected the tunnel. This might have been after the premature partial break-in and possibly also because of a small ‘man-hole’ opening which had been used to reconnoitre the position at night. The attackers concluded afterwards that they had detected this or the noise of the tunnelling, for the Turks directed heavy fire on the opening of the tunnel from the start of the attack:

…whether he had heard mining operations being carried out on the cliff or not cannot be definitely stated, but this fire was responsible for a great number of the casualties which we suffered. (Anon. Officer, 5th Battalion, Highland Light Infantry).²⁷

A portion of the Turkish trench was retained, but of those attacking from the tunnel one-third of the force, three officers and six other ranks, were killed. The survivors had mixed feelings about the value of the tunnel:

It was a great piece of engineering work and in some ways proved very useful when the attack was ultimately carried out, although in others it probably accounted for a number of the casualties which the battalion suffered.²⁸

It is a matter of speculation whether this experience contributed to caution in the use of Russian saps by VIII Corps when it reached the Western Front following evacuation from Gallipoli. The experiences of using tunnels for the assault on the peninsula highlighted the hazards of their use in the attack: emerging from a tunnel was highly dangerous as secrecy was very difficult to achieve if a tunnel was to be advanced close to the enemy positions. A rapid assault was also very difficult to achieve by men emerging from a small number of tunnel openings. On the Western Front the British developed the Russian sap as a means of reinforcing the position immediately after capture, rather than as a means of getting troops across no man’s land for the initial assault. Instructions for preparations to be made before large-scale attacks, issued by GHQ in February 1916, instructed that:

Saps must be pushed forward as far as possible to facilitate making communication trenches between the two opposing lines after the assault. The entrances to these saps should be dug under the front parapets and if time allows continued by making Russian saps instead of saps above ground.²⁹

These were considered necessary because very soon after an attack was launched the Germans would render no man’s land impassable with highly effective artillery barrages and British troops who might have gained the German front trench were cut off from reinforcement and supply. They were then highly vulnerable to counterattack, which would drive them from the captured positions. The Russian saps were designed to form a protected means of communication across no man’s land, either as a covered tunnel or broken out to form a trench. Two Russian saps were dug before the Hohenzollern attack of 2 March 1916 to prepare communication trenches to the flanking craters, and these were broken open as the attack began.

An ambitious scheme of Russian saps was prepared for the Somme offensive of 1 July 1916. Saps driven across no man’s land were to have mortar emplacements constructed in branches on either side and were to be opened out prior to zero hour. In the north 252 Tunnelling Company prepared twelve, requiring a large force of attached labour, and by April 1916 the Company had 1,900 infantry attached (see map). As the saps neared the German lines, work was ceased at night to prevent the Germans from detecting them, but patrols succeeded in locating the northernmost sap, from John Copse, and twice blew surface charges in an attempt to destroy it, killing nine men.³⁰ The Germans also directed shellfire at the saps, but despite detection the saps were completed on time.