On 25th August Hopton entered Cornwall after separating from the Marquis of Hertford following their failed attempts to secure Wiltshire, Dorset and Somerset. He first visited Sir Bevill Grenvile at Stowe then, after brushing aside Bullers's Militia, headed for Pendennis on September 24th to confer with Slanning before appearing voluntarily before the assizes at Truro. After his successful defence of his actions, recruiting began and that October the famous five regiments of Cornish foot were formed under Colonel William Godolphin, Sir Bevill Grenvile, Sir Nicholas Slanning, Colonel John Trevanion and Warwick, Lord Mohun.

Hopton first used them to make an unsuccessful attempt on Exeter then fell back on Plympton, took it, and invested Plymouth on December 1st. Later that month they took Alphington, Powderham and Topsham but failed to capture Exeter in a night attack. Their first field battle was Braddock (actually Pinnock) Down in January 1643 when Ruthin's forces were forced to flee back through Liskeard and on to Saltash, while the Earl of Stamford withdrew from Launceston. Slanning's regiment, along with those of Grenvile and Trevanion and half of the horse and dragoons, pursued Stamford while the rest followed up Ruthin.

Civil War Plymouth

Hopton, after some futile negotiations, invested Plymouth again and this led to Slanning's sole command in battle, but not until after the first ‘wheel’ was lost when the court poet Sydney Godolphin died of a wound received in a skirmish at Chagford. In February 1643 Slanning, in command of a detachment consisting of his and Trevanion's regiments, was attacked at Modbury by Chudleigh. He was able to execute that most difficult of manoeuvres, a fighting withdrawal against superior forces, but at the cost of 250 killed or wounded, 1,000 muskets and five guns.

The Cornish forces now quit Devon and things remained quiet until the extraordinary encounter battle of Polston Bridge, Launceston in April, when the arrival of Slanning's and Trevanion's regiments proved decisive. Two days later there was another encounter battle, the ‘Western Wonder’ of the Cavalier ballad, at Sourton Down, where in the middle of a violent thunderstorm, Chudleigh was able to hold the field and Hopton again retreated to Launceston.

Slanning and his men had a brief sojourn at Saltash before rejoining the rest in a rendezvous with Grenvile's foot. They brushed aside a small force at Week St. Mary on May 13th and at 5.00a.m. on the 16th attacked the forces on Stratton (now Stamford) Hill, Stratton. This produced their most spectacular victory when, after ten hours of fighting uphill against twice their number of much better equipped enemy with a dug-in battery, they gained the position, killing 300 and capturing 1,700 with fourteen guns, £300 and plentiful provisions, at a cost of 80 men. Slanning and Trevanion commanded the westernmost of the four columns.

The army was about to lose its independence though, and received orders to rendezvous with Prince Maurice's men, whom they met at Chard in Somerset in June. This combined force now took Taunton, Bridgwater, Dunster Castle and Wells. Their first contact with Waller was a cavalry skirmish at Chewton Mendip. He was driven out of Monkton Farleigh on July 3rd and two days later followed the pyrrhic victory of Lansdown where the next ‘wheel’, Sir Bevill Grenvile, fell. The foot were now besieged in Devizes but witnessed the destruction of Waller's forces at Roundway Down. The Western Royalists took Bath, and after joining Prince Rupert on July 26th 1643 they stormed Bristol. The Western Army attacked the South Eastern defences at 3.00a.m. in three tertia, one commanded by Slanning.

Bristol fell after some thirteen hours fighting, but so did the last two ‘wheels’: Slanning and Trevanion were both mortally wounded. Sir Nicholas Slanning, whose leg had been broken by a musket ball, died three weeks later, quipping “that he had always despised bullets, having been so used to them, and almost thought they could not hurt him”, and professing “great joy and satisfaction in the losing of his life in the King's service to whom he had always dedicated it”.

No record remains of where Sir Nicholas Slanning was buried. The Sir Nicholas Slanning buried at St Mary the Virgin at Bickleigh, Devon was ‘our’ Sir Nicholas's grandfather, but Slanning's body may have been returned there for burial since some of his arms reached Bickleigh and his helmet and gauntlet may still be seen, by arrangement, at the church.