During the Revolutionary War against the British Hazelwood played an important role in the planning of the various American river defenses.
During the months prior to the British advance on Philadelphia he oversaw the development and construction of fire-vessels, which were used in conjunction with the many river obstructions, Cheval de frise, that were also developed for use in the Delaware River.
The designs proved effective and in July, 1776, Hazelwood was immediately sent to Poughkeepsie, New York, (one among a committee of three) with orders to plan for and construct similar river obstructions to prevent British marine navigation on the upper Hudson River;
At the time Commodore John Barry was the senior navy captain in Philadelphia and the visible choice to command both the Pennsylvania and Continental navies, but command was given to Hazelwood, already in command of the Pennsylvania Navy.
Hazelwood was soon promoted to Commodore of both the Pennsylvania and Continental navies in the Delaware River some time in 1777 but the exact date is not known.

Hazelwood planned for and participated in the defense of the Delaware River approach to Philadelphia in 1777 before and during the Siege of Fort Mifflin, which lasted approximately three weeks.
He was soon appointed to oversee the building of and command of fire rafts, which were used to prevent passage of British ships bringing badly needed supplies to British in Philadelphia.
In planning for the fort's defense the Committee of Safety authorized the construction of war-ships, a flotilla of fire-rafts, floating batteries and the construction of river obstacles which were floated into place and sank.
Construction of ten fire-rafts reached completion by December 27 where Hazelwood was appointed commander of this fleet of rafts.
In the following May the Committee of Safety selected Hazelwood "to survey the river from Billingsport to Fort Island and the East side across from the island.

Hazelwood was given a scouting assignment on September 19, with orders to move the American fleet to Darby Creek to observe British strength, vessels and activity at Chester.
Various American rivercraft also engaged and harassed the British at various points along the river.
In the process Hazelwood obtained much information about the British presence, which was copied and passed on to other commanders in the greater area.

Philadelphia finally fell on September 26 and Vice Admiral Howe and the British army entered the city, however they were low on ammunition and supply and had not established a naval supply route along the heavily defended Delaware River.
In the days that followed the British began fortifying the shore surrounding the city and at the mouth of the Schuylkill River, bringing in heavy guns and supplies.
During October the American fleet engaged British naval vessels and gave support to American forts along the river.
Hazelwood frequently ordered galleys to deter British ships away from Billingsport.
Hazelwood's galleys kept up a disrupting fire while others patrolled the waters around Fort Mifflin.
On October 9, Hazelwood's fleet of galleys attacked the British battery at Webb Ferry.
Two days later, Hazelwood landed a body of militia on Carpenter's Island, assaulting the middle battery and capturing fifty men and two officers.
A second assault on British batteries was attempted the next day but was met with heavy fire, causing the American vessels to withdraw after receiving heavy losses.

On October 22 the British launched naval assaults on positions below the fort in concert with a ground assault on Fort Mercer.
In a letter of October 23, 1777, to General Washington, a fatigued Hazelwood reported that on that morning his fleet had driven the British fleet down river and forced one of its frigates ashore where the vessel accidentally exploded somehow.
He reported also that his fleet was in need of reinforcements but maintained that he would not draw any men from the fort, as they were badly needed there.
At this time the Marine Committee of Congress ordered Hazelwood and his sec
During the Revolutionary War against the British Hazelwood played an important role in the planning of the various American river defenses. During the months prior to the British advance on Philadelphia he oversaw the development and construction of fire-vessels, which were used in conjunction with the many river obstructions, Cheval de frise, that were also developed for use in the Delaware River. The designs proved effective and in July, 1776, Hazelwood was immediately sent to Poughkeepsie, New York, (one among a committee of three) with orders to plan for and construct similar river obstructions to prevent British marine navigation on the upper Hudson River;
At the time Commodore John Barry was the senior navy captain in Philadelphia and the visible choice to command both the Pennsylvania and Continental navies, but command was given to Hazelwood, already in command of the Pennsylvania Navy. Hazelwood was soon promoted to Commodore of both the Pennsylvania and Continental navies in the Delaware River some time in 1777 but the exact date is not known.
Hazelwood planned for and participated in the defense of the Delaware River approach to Philadelphia in 1777 before and during the Siege of Fort Mifflin, which lasted approximately three weeks. He was soon appointed to oversee the building of and command of fire rafts, which were used to prevent passage of British ships bringing badly needed supplies to British in Philadelphia. In planning for the fort's defense the Committee of Safety authorized the construction of war-ships, a flotilla of fire-rafts, floating batteries and the construction of river obstacles which were floated into place and sank. Construction of ten fire-rafts reached completion by December 27 where Hazelwood was appointed commander of this fleet of rafts. In the following May the Committee of Safety selected Hazelwood "to survey the river from Billingsport to Fort Island and the East side across from the island.
Hazelwood was given a scouting assignment on September 19, with orders to move the American fleet to Darby Creek to observe British strength, vessels and activity at Chester. Various American rivercraft also engaged and harassed the British at various points along the river. In the process Hazelwood obtained much information about the British presence, which was copied and passed on to other commanders in the greater area.
Philadelphia finally fell on September 26 and Vice Admiral Howe and the British army entered the city, however they were low on ammunition and supply and had not established a naval supply route along the heavily defended Delaware River. In the days that followed the British began fortifying the shore surrounding the city and at the mouth of the Schuylkill River, bringing in heavy guns and supplies. During October the American fleet engaged British naval vessels and gave support to American forts along the river. Hazelwood frequently ordered galleys to deter British ships away from Billingsport. Hazelwood's galleys kept up a disrupting fire while others patrolled the waters around Fort Mifflin. On October 9, Hazelwood's fleet of galleys attacked the British battery at Webb Ferry. Two days later, Hazelwood landed a body of militia on Carpenter's Island, assaulting the middle battery and capturing fifty men and two officers. A second assault on British batteries was attempted the next day but was met with heavy fire, causing the American vessels to withdraw after receiving heavy losses.
On October 22 the British launched naval assaults on positions below the fort in concert with a ground assault on Fort Mercer. In a letter of October 23, 1777, to General Washington, a fatigued Hazelwood reported that on that morning his fleet had driven the British fleet down river and forced one of its frigates ashore where the vessel accidentally exploded somehow. He reported also that his fleet was in need of reinforcements but maintained that he would not draw any men from the fort, as they were badly needed there. At this time the Marine Committee of Congress ordered Hazelwood and his sec
John Hazelwood