Since the 15th century, conventional explosives have been used in ever-increasing quantities against key targets. David Porter traces some of the most spectacular episodes in war on land, air, and sea.

Mine crater on Messines Ridge, Western Front, 1917.


Mining has been a feature of siege warfare since at least 700 BC. Until the end of the Middle Ages, it generally involved driving tunnels under enemy fortifications, which, once under the defences, were enlarged to form chambers, supported by wooden props. Brushwood was then stacked in the chambers and fired, to bring down a section of the walls. By the 15th century, gunpowder began to be used in military mines. The detonation of one of the first such mines during the Spanish siege of the Moorish city of Malaga in 1487 brought down a large tower. In 1495, Spanish engineers used a much larger mine to destroy an entire outwork of the French-held Castello Nuovo in Naples.

Contemporary plan of the mine under the Confederate trenches at Petersburg in June 1864.

Mining techniques were steadily refined. By the late 17th century, Vauban’s manuals of siege warfare included tables for mines using up to 12,000kg (26,455lb) of gunpowder to destroy entire fortresses. Similar techniques were in use well into the 19th century, notably at the Siege of Petersburg during the American Civil War, when besieging Union forces dug a tunnel 156 metres (511 feet) long under the Confederate lines, which was packed with 3,600kg (8,000lb) of gunpowder. When the mine was detonated on 30 July 1864, it destroyed a key sector of the Confederate defences, killed 278 men, and left a crater 50 metres long, 25 metres wide, and 10 metres deep.

The shocked defenders took at least 15 minutes to reorganise, giving Union forces a golden opportunity to break through to Petersburg. Incredibly, the chance was missed: in a classic case of ‘snatching defeat from victory’, the Union botched their attack.

Cross-sections through the Petersburg mine.


Brigadier-General Ferrero’s African-American division had been specially trained as assault troops. Crucially, their training stressed the importance of attacking immediately after the mine detonated to exploit the defenders’ confusion, and the need to avoid getting trapped in the mine crater.

At the last minute, General Burnside ordered that the African-Americans should not make the attack, as he was concerned about a storm of protest from press and politicians if they sustained heavy casualties. Another division was assigned instead. Lacking any special training, they were slow in making their attack, and then took cover in the crater where they were trapped by a prompt Confederate counter-attack launched on the initiative of the very able Brigadier-General William Mahone. His men lined the edge of the crater and fired down on the massed Union infantry in what Mahone later described as ‘a turkey shoot’.

Despite the obvious failure of the attack, Burnside sent in Ferrero’s men, who were forced into the crater by intense flanking fire and simply added to the horrendous Union casualties, which finally totalled 3,798 (504 killed, 1,881 wounded, 1,413 missing or captured), against a Confederate total of 1,491 (361 killed, 727 wounded, 403 missing or captured).


Technological advances in explosives and mining during the second half of the 19th century allowed mine warfare to reach a peak of sophistication during the First World War. The classic example was Messines Ridge, where 19 British mines with galleries up to 6580 metres (2,160 feet) long were dug in 1916/17 and filled with almost 600 tons of explosives in preparation for an offensive to take the ridge. After a final briefing, Major-General Harington remarked: ‘Gentlemen, we may not make history tomorrow, but we shall certainly change the geography.’

This famous photograph of the Hawthorne Ridge explosion in the Somme sector in 1916 gives a vivid impression of what the Messines detonations would have looked like.

All 19 mines were detonated within the space of 20 seconds on 7 June 1917. They blew the crest off the Messines-Wytschaete Ridge. At the time, the combined sound of the explosions was the loudest man-made noise in history and was clearly heard in London, although freak acoustics meant that many Allied troops in the immediate area only heard a ‘muffled roar’. Father William Doyle, chaplain of the 16th Irish Division, recalled that, ‘I saw seven huge columns of smoke and flames shoot hundreds of feet into the air, while masses of clay and stones, tons in weight, were hurled about like pebbles. I never before realised what an earthquake was like, for not only did the ground quiver and shake, but actually rocked backwards and forwards, so that I kept on my feet with difficulty.’


The lighting up of the sky as the detonations ran across the ridge was likened to a ‘pillar of fire’, and the effect on the German defenders was devastating. As individual mines were packed with
anything up to 43,450kg (95,600lb) of explosives, the craters they formed were huge, with diameters of up to 79 metres (260 feet). All German defences and personnel (possibly as many as 10,000 men) were ‘obliterated’ at distances up to 116 metres (380 feet) from the centres of the craters. The Germans’ deep concrete dug-outs were immune to all but direct hits from heavy artillery, but gave no protection from the enormous mines. The next day, Harington entered one such bunker and found four German officers sitting around a table ‘… all dead – killed by shock. It was an uncanny sight – not a mark on any of them.’

In marked contrast to the botched Union assault at Petersburg, the initial stages of the attack at Messines were exceptionally successful, thanks to meticulous planning and sophisticated tactics, which were a world away from the clumsy methods employed on the Somme less than a year earlier. The ridge itself was captured on the first day of the battle, when General Plumer’s Second Army advanced 4 kilometres (2.5 miles) on a 16-kilometre (10-mile) front.

One of the Messines Ridge mine craters.

Second Army’s casualties were far lower than expected on the first day of the offensive, largely due to the impact of the mines, which stunned the surviving German defenders. Resistance ‘hardened’ considerably as the attack continued, but even so, the final figures were 17,000 Allied casualties compared to 25,000 German (including 7,200 prisoners). A significant number of German weapons were also captured, including at least 48 guns, 218 machine-guns, and 60 mortars. Five other mines were prepared, but not detonated, as the Germans had retreatedfrom those sectors before the attack was made. One containing 12,000kg (26,000lb) of explosives detonated during a thunderstorm in 1955 when lightning struck an electricity pylon built over the site, but fortunately a cow was the only casualty. The remaining four, with explosive charges totalling 62,100kg (136,907lb), remain beneath the ridge…


The Spanish Netherlands (essentially modern Belgium and Holland) first rebelled against Spanish rule in 1565. Despite their battlefield superiority, Spanish forces were unable to achieve a decisive victory and became bogged down in prolonged siege warfare.

In 1585, their main field army, commanded by the Duke of Parma, was committed to the Siege of Antwerp. One of those who escaped from the city just before the siege was an Italian engineer,
Federigo Giambelli, who had moved to Antwerp after failing to interest Philip II of Spain in his inventions. Thereafter he harboured a bitter grudge against Philip and successfully petitioned Elizabeth I for funding to defend the city. Antwerp was surrounded by the Duke of Parma’s veteran Spanish army of 40,000 men. By February 1585, the city was completely sealed off by an enormous fortified 800-metre (875-yard) pontoon bridge across the Scheldt from Calloo to Oordam.

The bridge was defended by strong booms and seemed impregnable, but Giambelli came up with a solution – to convert two merchant vessels into floating ‘bombs’, filled with gunpowder
and fitted with delayed-action fuses. These ships would be released upstream of the bridge and drift downriver to detonate against the pontoons. Giambelli was allotted two ships each of
about 70 tons, the Hoop (‘Hope’) and the Fortuyn (‘Fortune’). Both were ‘gutted’ and packed with huge explosive charges – each ship carried about 3,175kg (7,000lb) of gunpowder, together with an assortment of rubble and scrap iron for greater lethality.

The Fortuyn was fitted with a conventional fuse using lengths of slow match (cord soaked in potassium nitrate), which would burn at an average rate of 305mm (1 foot) per hour. A far more sophisticated detonator was installed on the Hoop – a combined clockwork and flintlock mechanism made by an Antwerp clockmaker. Both vessels then had their upper decks rebuilt and covered with firewood to resemble conventional fireships.


Dutch ‘hellburners’ in action at Antwerp in 1585.

The ‘hellburners’ were sent into action on the night of 4/5 April 1585. The Dutch naval commander, Vice-Admiral Jacob Jacobsen, launched them from Fort Boerenschans together with 32 ordinary fireships. The fireships burned themselves out on the lines of pontoons moored to form a floating boom to protect the bridge. The Fortuyn ran aground on the west bank some distance from the bridge, but its enormous demolition charge failed to fully detonate and the relatively small explosion caused little damage to the besieging forces. The Hoop, however, penetrated a gap between the end of the boom and the west bank before ramming the bridge.

Encouraged by the apparent failure of the attack, Spanish troops boarded her in an attempt to put out the small fires on her decks before they could spread to the bridge. At this point the novel fuse operated perfectly: the ship and a 60-metre (66-yard) section of the bridge were destroyed in an explosion that killed at least 800 Spanish troops and wounded the Duke of Parma. This stunning success was wasted, as Jacobsen failed to follow up the attack with his relief fleet, and Antwerp was forced to surrender on 17 August 1585.


HMS Campbeltown after its successful ramming of the Normandie Dock gates.

The nearest equivalent in modern history was Operation Chariot, the raid on St Nazaire. On the night of 28 March 1942, the explosive-laden obsolete destroyer HMS Campbeltown formed the key element of a raiding force tasked with the destruction of the Normandie Dock, the only dry dock on the French Atlantic coast capable of accommodating the battleship Tirpitz.

Campbeltown was loaded with 24 Mark VII depth-charges containing a total of over 4 tons of amatol high-explosive and successfully rammed the dock gates. Her delayed-action depth-charges detonated several hours later, killing 360 Germans and thoroughly wrecking the Normandie Dock, which was put out of action until 1947.


A Tallboy bomb descends.

The Tallboy, or ‘Bomb, Medium Capacity, 12,000lb’, was a deep-penetration ‘earthquake bomb’ developed by the British aeronautical engineer Barnes Wallis and deployed by the RAF in 1944.

Wallis first summarised his ideas for this type of bomb in his 1941 paper ‘A Note on a Method of Attacking the Axis Powers’, which showed that a very large delayed-action bomb exploding deep underground next to a target would undermine the target’s foundations, as shock waves are transmitted through the ground more strongly than through air.

The original intention was to produce a 10-ton bomb, but development of this monster proved to be difficult and it was decided to concentrate initial efforts on Tallboy, a smaller, more manageable weapon. In early trials, the bomb showed a tendency to tumble, so the tail fins were redesigned to incorporate a slight twist so that the bomb spun as it fell, significantly improving accuracy.

Tallboy was designed to be dropped from an optimum altitude of 5,500 metres (18,000 feet) at a speed of 270km/h (170mph). Impacting at 1,210 km/h (750mph), it blew a crater 24 metres (80 feet) deep and 30 metres (100 feet) across. Penetration was an impressive 4.9 metres (16 feet) of concrete or 18 metres (60 feet) of earth.

Tallboys were first used operationally by the RAF’s 617 Squadron in an attack on the Saumur rail tunnel during the night of 8/9 June 1944. The tunnel, a vital route for German reinforcements heading to the Normandy front, was totally blocked by a single Tallboy, which penetrated the hillside and exploded in the tunnel about 18 metres (60 feet) below.

The Saumur Tunnel after being struck by a Tallboy bomb.

Thereafter, the bombs were increasingly used to destroy heavily fortified targets such as U-boat pens and V-weapon sites for the remainder of the war. In addition to these targets, 9 and 617 Squadrons dropped Tallboys in three attacks on the battleship Tirpitz, finally sinking her off Tromso, Norway with at least two direct hits on 12 November 1944.


Even before Tallboy became operational, there were concerns that it might be defeated by improved protection of ultra-high-value targets. As a result, work began on an enlarged version, the 10,000kg (22,000lb) Grand Slam, in July 1943, and the new weapon entered service in March 1945.

A Grand Slam bomb is loaded for use.

The sheer size and weight of the new bomb required additional modifications be made to the Lancaster – the bomb-bay doors had to be removed, together with the nose and mid-upper turrets, and some armour. More powerful 1,610hp Merlin 24 engines were fitted, driving paddle-bladed propellers to improve performance.

A total of 33 such aircraft were built under the designation Lancaster B.I Special, and it was found that they could reach a maximum altitude of 5,800 metres (19,000 feet) when carrying a Grand Slam. Although this was well below the optimum release-height, which Barnes Wallis calculated as 12,000 metres (40,000 feet), it was found to be adequate to destroy the relatively few high-value
targets left in the last few months of the war.

On 14 March 1945, the first operational Grand Slam was dropped on the Bielefeld railway viaducts by Squadron Leader Charles Calder of 617 Squadron. The bomb worked perfectly, blowing away the foundations of both viaducts and bringing down 61 metres (200 feet) of the western span (the goodstraffic bridge) and 79 metres (260 feet) of the eastern span (the passenger-train bridge).

The Grand Slam explosion on the Bielefeld railway viaducts.

Several more successful attacks were made on other railway bridges as the war ended, but a particularly spectacular raid on 27 March destroyed the massive Valentin U-boat construction bunker near Bremen. Direct hits by two Grand Slams blew in the 4.6-metre (15-foot) thick ferro-concrete roof, choking the assembly bays with 1,000 tons of debris.

David Porter worked at the Ministry of Defence for 30 years and is the author of nine Second World War books, as well as numerous magazine articles.