Palatinate campaign
In May 1620, James I was being strongly urged by popular opinion to defend the Protestant cause of his son-in-law, Frederick V, Elector Palatine. He allowed Count Dohna, the Palatine envoy, to levy a body of volunteers at his own cost, and to appeal for funds. Dohna, as paymaster, selected Sir Horace Vere, as commander; Buckingham had wanted the post for Sir Edward Cecil, and withdrew support from the expedition.
News arrived of the treaty of Ulm (23 June), between the union of Catholic princes and the League, preparing the way for a Catholic invasion of the Palatinate, and money came in more rapidly. On 9 July, Vere went to Theobalds to take leave of the king, and on 22 July the regiment, 2,200 strong, set sail from Gravesend to the Netherlands, to be escorted south into Germany and to the seat of war by a body of Dutch cavalry. By this time Vere was a professional soldier, even-tempered, brave and popular. The Earl of Essex was one of his lieutenants. Spinola was in the field with one army, Velasco on the way with another.
Vere's plan was to effect a junction with the Protestant force near Mannheim, under the Margrave of Ansbach. He marched through Wesel into the neighbourhood of Coblenz, and then made a detour by a route through the Taunus, on the other side of which, in the valley of the Main River, Spinola made an unsuccessful attempt to cut him off. Vere crossed the Main by a ford, near Frankfurt, and then, by way of Darmstadt and Bensheim (there resting his troops), and proceeded to Worms, where the junction of forces actually took place.
Spinola now adopted Fabian tactics in the hope of wearing the enemy out, until the approach of winter compelled the English and their allies to seek quarters. Vere divided his troops among the three most important strongholds of the Palatinate. He himself occupied Mannheim, Gerard Herbert he stationed in Heidelberg Castle, while Sir John Burroughs undertook to defend Frankenthal.
Early in 1621, the Protestant Union was broken up, and the English garrisons had to give up all hope of relief. The English governors were not closely pressed that year. The garrison under Vere at Mannheim received a visit early in 1622 from the dethroned elector, who had promised them a diversion, and who, in conjunction with Mansfelt, had inflicted a momentary check upon the imperialist army under Johann Tserclaes von Tilly at Wiesloch (April). A few weeks later, however, Tilly, having been reinforced by Gonzalo Fernández de Córdoba, inflicted defeats on the Protestants, and in June the elector had finally to leave Mannheim.
The English garrisons were now surrounded and threatened by a force of imperialists and Spaniards under Tilly, Cordova, and Verdugo. Vere resolved to hold out, though he knew that the military position was hopeless. On 16 September, the town of Heidelberg was taken by storm, and the castle surrendered three days later. Sir Gerard Herbert had received a mortal wound during the siege. At Mannheim Vere, with a garrison of fourteen hundred men, without money or supplies, had to defend extensive fortifications. He retired to the citadel, but no extraneous help being forthcoming, he was forced to capitulate at the close of September, and, having marched out with the honours of war, withdrew to The Hague. Vere's defence was commemorated by George Chapman
At Frankenthal, Burroughs did not surrender the place to Verdugo until 14 April 1623, and then only in response to direct orders from home.
The courage displayed by Vere against great odds was recognised in England, when the general returned early in February 1623, even if his salary and expenses were never paid in full by the treasury. On 16 February 1623, he was appointed master-general of the ordnance for life, and he became a member of the council of war on 20 July 1624. On the death of his elder brother, John, in the same year he became his residuary legatee, with the reversion of Tilbury and Kirby Hall upon the death of the widow.