For prosecuting the campaign of 1778 Washington had not been provided with an adequate force. The committee of Congress who visited the army at Valley Forge had agreed that the army should consist of about 40,000 men, besides artillery and horse. In May (1778) the army, including the detachments at different places, was found to amount only to 15,000, with little prospect of increase. At Valley Forge Washington had 11,800. The British army at this time numbered 33,000. With such odds the plan of operations for this season must necessarily be defensive.

From the position which Washington had taken at Valley Forge, and from the activity and vigilance of his patrols, the British army in Philadelphia was straitened for forage and fresh provisions. A considerable number of the people of Pennsylvania were well affected to the British cause and desirous of supplying the troops, while many more were willing to carry victuals to Philadelphia, where they found a ready market and payment in gold or silver, whereas the army at Valley Forge could pay only in paper money of uncertain value. But it was not easy to reach Philadelphia nor safe to attempt it, for the American parties often intercepted and took the provisions without payment and not unfrequently chastised those engaged. The first operations on the part of the British, therefore, in the campaign of 1778, were undertaken in order to procure supplies for the army. About the middle of March a strong detachment, under Lieutenant-Colonel Mawhood, made a foraging excursion for six or seven days into Jersey, surprised and defeated the American parties at Hancock's and Quinton's bridges on Always creek, which falls into the Delaware to the south of Reedy Island, killed or took fifty or sixty of the militia prisoners, and after a successful expedition returned to Philadelphia with little loss.

A corps of Pennsylvania militia, daily varying in number, sometimes not exceeding fifty, sometimes amounting to 600, under General Lacey, had taken post at a place called Crooked Billet, about seventeen miles from Philadelphia on the road to New York, for the purpose of intercepting the country people who attempted to carry provisions to the British army. Early on the morning of the 4th of May, Colonel Abercrombie and Major Simcoe, with a strong detachment, attempted to surprise this party, but Lacey escaped with little loss, except his baggage, which fell into the hands of the enemy.

On the 7th of May the British undertook an expedition against the galleys and other shipping which had escaped up the Delaware after the reduction of Mud Island, and destroyed upward of forty vessels and some stores and provisions. The undisputed superiority of the British naval force and the consequent command of the Delaware gave them great facilities in directing a suitable armament against any particular point, and the movements of the militia, on whom Congress chiefly depended for repelling sudden predatory incursions and for guarding the roads to Philadelphia, were often tardy and inefficient. The roads were ill guarded, and the British frequently accomplished their foraging and returned to camp before an adequate force could be assembled to oppose them.

To remedy these evils—to annoy the rear of the British troops in case they evacuated Philadelphia, which it was now suspected they intended to do, and also to form an advanced guard of the main army—Lafayette, with upward of 2,000 chosen men and six pieces of artillery, was ordered to the east of the Schuylkill, and took post on Barren Hill, seven or eight miles in advance of the army at Valley Forge. Sir William Howe immediately got notice of his position and formed a plan to surprise and cut him off. For that purpose a detachment of 5,000 of the best troops of the British army, under General Grant, marched from Philadelphia on the night of the 20th of May and took the road which runs along the Delaware and consequently does not lead directly to Barren Hill. But after advancing a few miles the detachment turned to the left, and proceeding by White Marsh passed at no great distance from Lafayette's left flank and about sunrise reached a point in his rear where two roads diverged, one leading to the camp of the marquis, the other to Matson's ford, each about a mile distant. There General Grant's detachment was first observed by the Americans, and the British perceived by the rapid movements of some hostile horsemen that they were seen. Both Lafayette's camp and the road leading from it to Matson's ford were concealed from the British troops by intervening woods and high grounds. General Grant spent some time in making dispositions for the intended attack. That interval was actively improved by Lafayette, who, although not apprised of the full extent of his danger, acted with promptitude and decision. He marched rapidly to Matson's ford, from which he was somewhat more distant than the British detachment, and reached it while General Grant was advancing against Barren Hill in the belief that Lafayette was still there. The Americans hurried through the ford leaving their artillery behind, but on discovering they were not closely pursued some of them returned and dragged the field pieces across the river; a small party was also sent into the woods to retard the progress of the British advanced guard, if it should approach while the artillery was in the ford.

On finding the camp at Barren Hill deserted General Grant immediately pursued in the track of the retreating enemy toward Matson's ford. His advanced guard overtook some of the small American party, which had been sent back to cover the passage of the artillery, before they could recross the river and took or killed a few of them, but on reaching the ford General Grant found Lafayette so advantageously posted on the rising ground on the opposite bank and his artillery so judiciously placed that it was deemed unadvisable to attack him. Thus the attempt against Lafayette failed, although the plan was well concerted and on the very point of success. In the British army sanguine expectations of the favorable issue of the enterprise were entertained, and in order to insure a happy result a large detachment, under General Grey, in the course of the night took post at a ford of the Schuylkill, two or three miles in front of Lafayette's right flank, to intercept him if he should attempt to escape in that direction, while the main body of the army advanced to Chestnut Hill to support the attack, but on the failure of the enterprise the whole returned to Philadelphia.

General Grant's detachment was seen by Washington from the camp at Valley Forge about the time it was discovered by the troops at Barren Hill, alarm guns were fired by his order to warn Lafayette of his danger, and the whole army was drawn out to be in readiness to act as circumstances might require. The escape of the detachment was the cause of much joy and congratulation in the American and of disappointment and chagrin in the British army.

That a strong detachment of hostile troops should pass at a small distance from Lafayette's flank and gain his rear unobserved seems to argue a want of due vigilance on the part of that officer, but a detachment of the Pennsylvania militia had been posted at a little distance on his left and he relied on them for watching the roads in that quarter. The militia, however, had quitted their station without informing him of their movement, and consequently his left flank and the roads about White Marsh remained unguarded.

This was the last enterprise attempted by Sir William Howe. Soon after he resigned the command of the army. So far back as the month of October in the preceding year he had requested to be relieved from the painful service in which he was engaged. On the 14th of April, 1778, he received the King's permission to resign, but at the same time he was directed, while he continued in command, to embrace every opportunity of putting an end to the war by a due employment of the force under his orders. In the beginning of June after having received, in a triumphal procession and festival, a testimony of the approbation and esteem of the army he sailed for England, leaving the troops under the care of Sir Henry Clinton as his successor.

Sir William Howe has been much blamed for inactivity and for not overwhelming the Americans, but he was at least as successful as any other general employed in the course of the war. He was cautious and sparing of the lives of his men. In his operations he discovered a respectable share of military science, and he met with no great reverses. They who blame him for want of energy may look to the history of Generals Burgoyne and Cornwallis for the fate of more enterprising leaders in America.