Well, Terry, thanks to GLS we've now got some documentation of major failure of siege mortars in battle. The Allied (British and French) artillery assault on Sweaborg in the Crimean War. The majority of the British large iron mortars were damaged in use during the attack.
CRIMEAN WAR "The conflagration had, in fact, spread beyond the island of Vargon, and had extended to East Svarto, in its rear. During the whole night of the 10th, a heavy fire was kept up; and, upon the recall of the gunboats as before, divisions of mortar-boats again proceeded to annoy the enemy. One division, directed by Captain George Henry Seymour, of the Pembroke, was under the orders of Lieutenants Robert James Wynniatt, and James Carter Campbell (Exmouth), Charles Maxwell Luckraft (Euryalus), Henry Bedford Woolcombe, and Cornwallis Wykeham Martin (Arrogant), John Binney Scott, and Francis Moubray Prattent (Pembroke), and Henry Bartlett King (Magicienne}. The other division, directed by Captain Caldwell, was under the orders of Lieutenants Leveson Eliot Henry Somerset, and Thomas Barnardiston (Duke of Wellington), John Appleby Pritchard, and William Hans Blake (Edinburgh), Robert Boyle Miller (Vulture), and John Bousquet Field (Cossack), assisted by junior officers. In the course of the night, seeing that nearly every building on Vargon had been destroyed, and that such buildings as remained standing on East Svarto were almost, if not quite, out of range, while the enemy scarcely returned the fire, the allied Admirals agreed to discontinue the action before daylight on the 11th.
By that time, most of the mortars had been disabled, and two, if not three, completely split ("It is a disgrace to our iron-founders that one old mortar of the last war stood 350 rounds, while all the others, quite new, were unfit for use, or burst, after 200 to 250", Sulivan); and the vents of some of the French guns employed in the attack had fused. There were, unfortunately, no spare mortars, owing to lack of prevision at home. There had, however, been singularly few casualties on the side of the attack, only one man, it is said, having actually lost his life. The British alone had expanded in the bombardment about 100 tons of powder, and 1000 tons of projectiles (the French mortars threw 2828 shells, and the French vessels, apart from the mortar-vessels, 1322 shells and round shot)."
"The allied fleets remained in view of the scene of action until the morning of August 13th, when they sailed for Nargen, the Merlin and Locust staying behind to take up buoys and marks.
A few days later, there being practically no mortars left in a serviceable condition, the mortar-vessels were sent home. At the same moment the Sans Pareil was taking on board fresh mortars at Woolwich; but Dundas was not kept informed of what was being done. When it became known at Whitehall that the mortar-vessels were returning, a steamer was hastily despatched to meet them, and turn them back; but ere they could be re-armed, the season was too far advanced for further operations of importance in the Baltic. As the Times said, a fleet costing about .£30,000 a day for maintenance was reduced to impotence, and made a laughing-stock, in consequence of the Government's omission to spend at the right moment "about as much as a man of taste gives for three early Sevres vases." The administration seems to have forgotten that ships cannot participate in big engagements without expending weapons as well as ammunition. In future naval wars, especially if they be prolonged, it will be more than ever necessary to have made arrangements beforehand for the rapid substitution of new guns for old. Moreover, nothing is more dangerous to the moral of a gun's crew than a well-founded suspicion that the piece has already done more work than it was intended for, and may burst, or blow its breech-block out, at the next round. Yet it is difficult to avoid using a weakened gun, when there is nothing to take its place."
