The besiegers still continued their bombardment of the House but without much effect; and the garrison continued to have much the best of the sorties. On the morning of Wednesday, April 11, Captain Farmer and Captain Radcliffe led out about half the garrison from a postern gate and drove the Parliamentarians from most of their works, which had now been formed all round the walls, Radcliffe showing especial bravery. The retreat was secured by Captain Ogle and Captain Chisenhale. The royalists declared that they had spiked all the besiegers' guns, but as the bombardment continued after this without any intermission the statement must be false. They were evidently obliged to take great precautions against the cannon shot, and men were constantly on the watch with damp cloths to prevent the buildings from catching fire. Towards the middle of April a chance shot entered the window of Lady Derby's room "but was too weak to fright her from the lodging"; ten days afterwards, however, two larger cannon bullets broke into the room, and she was obliged to remove to another part of the building. The royalists were most in fear of the large mortar piece; and their next expedition was made with the object of effecting its capture. About 4 a.m. on April 26th,[130] a sortie in force was made. The walls and gates were well guarded, and a reserve told off to assist a retreat if necessary; Captain Chisenhale then issued from the eastern gate, surprised the besiegers and after severe fighting drove them from their trenches. The great cannon was placed upon a sledge which had been kept in readiness and drawn within the walls. The Parliamentarians must have suffered considerably in this skirmish, and they lost still more in prestige. Inside Lathom there were extravagant expressions of joy at the capture of the dreaded mortar; and the royalists boasted that the very day of its capture Rigby had invited a number of his friends to witness the surrender of the House. The besiegers were proportionately discouraged by its loss; and many of their other guns were now removed in order to prevent their capture.
The Parliamentarians now endeavoured to cut off the water supply from Lathom and to drain the moat. The first was impossible, as the springs that supplied the well inside Lathom were drawn from higher ground east of the House. A trench was begun in order to empty the moat, but it does not seem to have been proceeded with. The country people of the neighbourhood were pressed into service, and many weeks' work was spent in vain. The fidelity of the chief engineer, whose name was Brown, was by no means above suspicion, and he was at any rate incompetent if not treacherous. In one of the sorties by the garrison an assistant engineer was taken prisoner, and he explained the design of the trench.