Hydrography

What the heck is Hydrography?


This past week we celebrated "world hydrography day," so I thought I would reflect on this little-known science's relevance to the American War for Independence. Let's start with the definition of hydrography: the science that deals with the measurement and description of the physical features of oceans, lakes, rivers, seas, and their adjoining coastal areas, particularly regarding their use for navigational purposes. Although the formal science of hydrography was not established until the latter part of the 18th century (by the French), assessments of waterways had been essential to the safety of navigation for many centuries prior, particularly beginning with the Age of Exploration. Throughout the American Revolution, those watermen who had intimate knowledge of the coastlines, rivers, and estuaries were critical to both sides, but especially the British, who depended on the Royal Navy for its strategic advantage.

1571 pre-Mercator nautical chart from Portuguese cartographer
Fernao Vaz Dourado

Knowledge of the waterways and shorelines around Boston, New York, Philadelphia, Wilmington, and Charleston played a critical role for warships, merchant vessels, smugglers, and privateers. This was especially true for the rebels, whose use of small craft and longboats was often their only defense against the wide array of British ships. Local ferrymen, fishermen, and pilots were crucial, and both sides competed for their services and loyalty. A failure to understand the features above and below the water, as well as the local tides, often led to disasters, both large and small. In ancient (and perhaps not so ancient) times, mariners called on Neptune, the god of the sea, for assistance when their knowledge of the tides and shoals failed them. Here are some tales of Neptune's influence on the struggle for independence...


The First Affair


The grounding of a ship in the lead-up to the American Revolution is a prime example of the impact of hydrography. The so-called Gaspee Affair took place on June 9, 1772. The HMS Gaspee, a British customs ship, ran aground in Rhode Island, where a group of Sons of Liberty attacked and set fire to the vessel. The British government threatened to send the American perpetrators for trial in England, but no arrests were made. Nevertheless, their threat to send Americans for trial in England sparked alarmed protests in the colonies, which were informed of the affair by the Committees of Correspondence. The establishment of the permanent Committees of Correspondence led to the founding of the First Continental Congress and ultimately to the Declaration of Independence.

Grounding and burning of the Gaspee - prelude to war

Gloucester


Neptune works both ways—he rarely takes sides. The Battle of Gloucester serves as an example. It was a skirmish fought early in the American Revolutionary War (August 8 or 9, 1775) at Gloucester, Massachusetts. Royal Navy Captain John Linzee, commanding the sloop-of-war HMS Falcon, spotted two schooners returning from the West Indies. After capturing one schooner, Linzee chased the second (American) into Gloucester Harbor, where it ran aground. Linzee sent sailors to seize the prize. However, the townspeople called out their militia, who captured the British seamen sent to take the grounded vessel. The militia also recovered the ship. Local knowledge of the waters around Boston provided an invaluable advantage to the New Englanders who faced off against the powerful land and naval forces throughout that pivotal year.

Massachusetts coastline

Aside from this incident, Gloucester is renowned for being the home of the legendary regiment of Marblehead sailors, whose expertise and skill in navigating coastlines and riverways played a crucial role in rescuing the Continental Army from destruction and enabling Washington's Christmas night crossing of the Delaware River, which led to a stunning blow for freedom at Trenton.

Marblehead Sailors' helped save the revolution

HMS Somerset vs Neptune

The HMS Somerset began its service in the American Revolution by shelling Charlestown in 1775. The Somerset had great success operating in estuaries, bays, and rivers. It served as the flagship headquarters at Bunker (Breed's) Hill.

Knowledge of waterways was critical for large ships of war

The Somerset was involved in another brief but important incident during the war, the Battle of Chelsea Creek. On the night of May 27, 1775, the armed schooner HMS Diana ran aground in Chelsea Creek while attempting to prevent Americans from driving British livestock off Noddle's Island in Boston Harbor. The American rebels set fire to the ship. HMS Somerset's tender, Britannia, was able to rescue the crew of the Diana. Later, it took part in the ferocious river fighting at Fort Mifflin near Philadelphia.

HMS Somerset

The battle for Fort Mifflin involved ships and boats navigating the treacherous waters of the lower Chesapeake River. It was a desperate, drawn-out siege, featuring land and naval forces that leveraged the elements and geography to their advantage. The Somerset participated in the later phase, bombarding the fort from far offshore. Meanwhile, other small vessels navigated dangerous waters in the ebb and flow of fierce combat that lasted for weeks. To prevent the British from using two nearby islands, the Americans breached the riverside dikes. 

This action forced the British to construct their batteries on top of the dikes and to work in knee-deep water. As an illustration of the challenges faced, the British lost an 8-inch howitzer and a soldier drowned when the craft carrying the gun sank in the Schuylkill. While bombarding Fort Mifflin, the Augusta and Merlin ran aground. A high tide occurred that evening, but contrary winds hindered the depth required for the ships to be freed. On October 23, 1777, the American forts focused their fire on the two stranded ships. HMS Isis maneuvered alongside the grounded sixty-four in a rescue attempt. British accounts claimed that American gunnery caused only minor damage, though flaming wads from the ships' guns ignited Augusta. At midday, the Augusta exploded in a tremendous blast that shattered windows in Philadelphia. An eyewitness reported that 60 sailors, a lieutenant, and the ship's chaplain perished while struggling in the water. The loud explosion was heard nearly 30 miles away in Trappe, Pennsylvania. After the Augusta's destruction, the crew of the Merlin set their ship on fire and abandoned it.

British bombard Fort Mifflin

But Neptune's favor for Somerset ended when she ran aground off Provincetown in 1778. Over 100 of her men were taken prisoner by angry locals who forced them to walk back to Boston, a distance of more than 125 miles! The wreck of the Somerset revealed itself in those waters after a storm in 1886, and again in January 2008.

Knowledge of the tides and shoals was critical around New York

New York, New York

When the British drove the Continental Army out of New York City in 1776, their knowledge of the waterways and islands became crucial. Although they had no shortage of sympathizers familiar with the waters, so did the Americans. The farther the British ventured from the "safe zone" of New York Island (Manhattan) and Long Island, the more precarious the situation became. In 1776, thwarting an attempt at naval envelopment, the rough shoreline and waters of the Bronx forced General Howe to try landing further north near Pelham. This delay allowed the Americans to shift forces to protect the Continental Army and maintain their line of communication.

The British landed at Pelham when the  shoals near
Throg's Neck proved unmanageable

The coves along the north shore of Long Island allowed rebels to slip boats in and out without (usually) risking detection. This facilitated one of George Washington's more famous spy rings in passing intelligence across the Long Island Sound to American-controlled Connecticut (where knowledge of the cost proved equally important). During the time of the War of Independence, the great Sandy Hook was more than just the peninsula we see extending from the Jersey shore today. The "hook" stretched across the mouth of the harbor as a massive sandbar, preventing ships of the line and frigates from passing in or out of Lower New York Bay except at high tide. This limited British options when they needed to put ships to sea quickly. Later in the war, a French fleet abandoned the notion of an attack on New York for the same reason.

Vessels in New York Harbor had to wait for the tide to rise

The Carolinas  


In the Cape Fear area near Wilmington, North Carolina, superior knowledge of the coastal and inland waterways allowed the rebels to prevent reinforcements by sea, keeping the critical state in American hands from February 1777 until a second invasion force of British troops arrived in 1780. This marked the beginning of a prolonged guerrilla-style war along the treacherous Cape Fear River. British warships patrolled while blockade runners tried to smuggle invaluable supplies. Both sides relied on local knowledge of the waterways to achieve success.

In the savage guerrilla war along North Carolina's coast,
both sides needed knowledge of the waterways

William Moultrie 

In neighboring South Carolina, local knowledge of the waterways and swamps in the Lowcountry played a significant role in the struggle. The partisans along the coastal rivers proved to be a constant thorn in the side of the British, who needed two attempts to capture the port of Charleston. In the first attempt in 1776, famed South Carolinian William Moultrie's clever defense, along with the geography of the islands and waters, held off a large British force of warships and soldiers. A key to his success was the use of palmetto logs for the fort. The palmetto is very porous (spongy), and each time the British fired a cannon, the ball would get stuck in the fort and wouldn’t explode. If it did explode, the fort's sand walls would collapse and smother the fire. Confused by the fact that the fort wasn’t burning, the British moved in closer. Bad idea. Three of His Majesty’s ships ran aground on a sandbar, which is now the location of Fort Sumter. There, they became sitting ducks for patriots. Francis Marion, who would later become famous as the “Swamp Fox," ordered the fort's guns to be turned on those ships. The British managed to save two of the ships, but a third was lost.

British naval map of Sullivan Island defenses