On Oct. 13, 1775 — nearly nine months before the nation declared its independence from the British Empire — the Second Continental Congress authorized the creation of the Continental Navy.

Plans called for the construction of 13 frigates by shipbuilders scattered around the colonies, but constructing warships from scratch would take time.

To provide an immediate force, Congress merely had to look at the commercial docks in Philadelphia to find vessels and men suitable for transforming into warships and sailors.

American merchant ships and their mariners adopted the banner of the Continental Navy. Men such as John Paul Jones and John Barry achieved success as naval officers after relinquishing their commercial profession.

On April 30, 1798, after attacks against American merchant ships off the North African coast, the Congress made the Navy into a separate cabinet department. Previously, naval matters were handled solely by the War Department.

President John Adams selected a merchant, Benjamin Stoddert, as the nation’s first Secretary of the Navy.

He soon found himself in an undeclared naval war with France. The Navy’s initial actions involved convoying commercial ships in the Caribbean Sea to protect them from French privateers and across the Mediterranean Sea to ward off Barbary pirates.

When war was declared in 1812 against Great Britain, American commercial ships licensed as privateers outnumbered our warships and achieved the greatest success against British commerce.

During America’s Civil War, the nation’s private fleet began a decline in numbers, yet it proved instrumental to the success of the Union cause. More than half of the Navy’s ships, four-fifths of its officers and five-sixths of the sailors serving on blockade duty arrived from the merchant service.

After the Confederate surrender in 1865, the nation turned inward and allowed its Navy and merchant marine to decline.

That became a chronic problem in 1914, when the United States declared its neutrality upon the outbreak of World War I. Vessels carrying the American trade that were registered in Britain, Germany and other powers at war were diverted, converted for military missions or sought ports of refuge.

In United States, goods piled up in warehouses and upon the docks. Charter rates for ships increased twenty-fold, all because the American merchant marine only accounted for 11 percent of the world’s fleet.

The Shipping Act of 1916 aimed to fix this by safeguarding an American merchant marine that would serve the needs of both national security and commerce.

The United States Shipping Board created by the legislation was authorized to build and equip vessels — preferably in American shipyards — to become naval auxiliaries and troop transports while also constructing, leasing or chartering commercial shipping.

After the armistice, Congress crafted more legislation to ensure that the nation never again had to seize, requisition or borrow a fleet in time of war or peace.

The Merchant Marine Act of 1920, commonly referred to as the Jones Act, aimed to cement the relationship between the merchant marine and the military.

It ensured the operation of American ships on certain international routes and provided protection for the coastwise trade, known as cabotage.

When the United States went to war in 1917, the coastwise fleet transported the 1st Expeditionary Division to France on 14 ships of the American merchant marine. Eleven of them were drawn from the coastal trade.

The Jones Act ensured that a fleet of American ships remained in service along the coast and inland waters of the nation.

In the depths of the Great Depression and with war clouds brewing in Europe and Asia, Congress passed the Merchant Marine Act of 1936 to jump-start American shipbuilding.

This law ensured there were suitable American-flagged ships to pick up the slack should commercial vessels again be diverted across the globe.

In 1939, the ocean liner America — the first of more than 5,000 commercial ships built by the Maritime Commission — slid down the ways at the Newport News Shipbuilding Company, followed by troopships, freighters and tankers required to convoy the Arsenal of Democracy across the contested seas of the Atlantic and Pacific.

When the war ended in 1945, the United States was the world’s supreme thalassocracy.

The Merchant Ship Sales Act of 1946 provided vessels to war-torn commercial fleets around the world until they could build replacements.

In 1949, the new Department of Defense consolidated its military sealift function under the Military Sea Transportation Service (MSTS).

Today, out of the 289 ships in the Navy, one in five is manned and operated by the successor to MSTS, Military Sealift Command, which also maintains prepositioned ships with equipment necessary for Marine and Army brigades in the Indian and Pacific Oceans.

To surge more materiel to troops overseas, the Maritime Administration’s Ready Reserve Force oversees another 46 vessels.

And backing up these ships are 180 deep draft vessels of the American merchant marine ready to provide sustainment for the military. Just shy of 100 of them are engaged in coastal operations, providing the necessary billets for licensed mariners in the event war breaks out and their vessels are diverted to military missions.

In the international trade, American shipping companies provide the necessary global supply networks to flow the needed sustainment for American forces deployed overseas. During Operations Enduring Freedom and Iraqi Freedom, it was a combination of these three elements — prepositioning, surge and sustainment — that allowed American forces to deploy and operate in Afghanistan and Iraq.

Recently, two reports by the Center for Strategic and Budgetary Assessments highlighted the relationship between the Navy and the merchant marine.

In March, National Security Contributions of the U.S. Maritime Industry discussed its current state, with a focus on the ships, shipbuilding and ship repair capability, and current legislation that helps maintain this critical capacity.

It was followed by Sustaining the Fight: Resilient Maritime Logistics for a New Era. It highlighted the challenges the military will face in sustaining the necessary logistics for potential future conflicts against Russia or China.

Issues such as shortages in ships and mariners, lack of force protection for merchant ships and the age and decline in readiness of the government-owned sealift fleet are all identified.

Without the continued support of the Maritime Security Program (to maintain the ships earmarked for sustainment), cargo preference (to deliver military and other government cargo, including food aid), and the Jones Act (to make sure a domestic fleet is available in time of national crisis, with mariners to crew the surge fleet), the shortages and dangers cited by the CSBA will become insurmountable and endanger the ability of the nation to defend itself and the military to perform its missions.

Throughout the nation’s history, the Navy and merchant marine served as complementary forces.

The flag of the merchant marine reads “In Peace and War." That reflects the dual nature of the merchant marine — to support the nation’s trade during times of peace but to switch into a supporting role in time of war and steam into harm’s way.

And that’s why its nickname is “The Fourth Arm of Defense.”

Salvatore R. Mercogliano is a professor at Campbell University and teaches courses in World Maritime History and Maritime Security. He is also an adjunct professor with the U.S. Merchant Marine Academy and offers a graduate level course in Maritime Industry Policy. A former merchant mariner, he sailed and worked ashore for the U.S. Navy’s Military Sealift Command. His book, Fourth Arm of Defense: Sealift and Maritime Logistics in the Vietnam War, is available through U.S. Naval History and Heritage Command. His views do not necessarily reflect those of Navy Times or its staffers.