The military errors of Essex were probably in some degree produced by political timidity. He was honestly, but not warmly, attached to the cause of the Parliament; and next to a great defeat he dreaded a great victory. Hampden, on the other hand, was for vigorous and decisive measures. When he drew the sword, as Clarendon has well said, he threw away the scabbard. He had shown that he knew better than any public man of his time how to value and how to practise moderation. But he knew that the essence of war is violence, and that moderation in war is imbecility. On several occasions, particularly during the operations in the neighbourhood of Brentford, he remonstrated earnestly with Essex. Wherever he commanded separately, the boldness and rapidity of his movements presented a striking contrast to the sluggishness of his superior.
In the Parliament he possessed boundless influence. His employments towards the close of 1642 have been described by Denham in some lines which, though intended to be sarcastic, convey in truth the highest eulogy. Hampden is described in this satire as perpetually passing and repassing between the military station at Windsor and the House of Commons at Westminster, as overawing the general, and as giving law to that Parliament which knew no other law. It was at this time that he organized that celebrated association of counties to which his party was principally indebted for its victory over the King.
In the early part of 1643, the shires lying in the neighbourhood of London, which were devoted to the cause of the Parliament, were incessantly annoyed by Rupert and his cavalry. Essex had extended his lines so far that almost every point was vulnerable.
The young prince, who, though not a great general, was an active and enterprising partisan, frequently surprised posts, burned villages, swept away cattle, and was again at Oxford before a force sufficient to encounter him could be assembled.
The languid proceedings of Essex were loudly condemned by the troops. All the ardent and daring spirits in the parliamentary party were eager to have Hampden at their head. Had his life been prolonged, there is every reason to believe that the supreme command would have been intrusted to him. But it was decreed that, at this conjuncture, England should lose the only man who united perfect disinterestedness to eminent talents, the only man who, being capable of gaining the victory for her, was incapable of abusing that victory when gained.
In the evening of the seventeenth of June, Rupert darted out of Oxford with his cavalry on a predatory expedition. At three in the morning of the following day, he attacked and dispersed a few parliamentary soldiers who lay at Postcombe. He then flew to Chinnor, burned the village, killed or took all the troops who were quartered there, and prepared to hurry back with his booty and his prisoners to Oxford.
Hampden had, on the preceding day, strongly represented to Essex the danger to which this part of the line was exposed. As soon as he received intelligence of Rupert's incursion, he sent off a horseman with a message to the General. The cavaliers, he said, could return only by Chiselhampton Bridge. A force ought to be instantly despatched in that direction for the purpose of intercepting them. In the meantime, he resolved to set out with all the cavalry that he could muster, for the purpose of impeding the march of the enemy till Essex could take measures for cutting off their retreat. A considerable body of horse and dragoons volunteered to follow him. He was not their commander. He did not even belong to their branch of the service. But "he was," says Lord Clarendon, "second to none but the General himself in the observance and application of all men." On the field of Chalgrove he came up with Rupert. A fierce skirmish ensued. In the first charge Hampden was struck in the shoulder by two bullets, which broke the bone, and lodged in his body. The troops of the Parliament lost heart and gave way. Rupert, after pursuing them for a short time, hastened to cross the bridge, and made his retreat unmolested to Oxford.