The US Navy's Ohio-class nuclear-powered submarines are among the most powerful submarines in the world, and recently have been increasing their presence in the Indian Ocean.
For the first time, an Ohio-class ballistic missile submarine docked at the remote island of Diego Garcia as part of an extended months-long deployment, US Strategic Command (STRATCOM) announced in a December 7 statement.
The USS West Virginia made the port visit October 25-31, the statement said.
The movements of the Navy's nuclear submarines are highly classified, so the delayed announcement would have given the submarine the time to head to other locations in the Indian Ocean, CNN reported.
The significance of publicising the port call of the USS West Virginia is to send a message to potential adversaries as well as to allies, a military official familiar with the unusual port stop told CNN.
"They should take from this that a ballistic missile submarine which is undetectable can operate in any ocean for an extended period," the official said.
Diego Garcia is an overseas territory of the United Kingdom south of the equator that is used by both US and British forces.
The submarine conducted a complete crew exchange while at the island and a subsequent replenishment at sea, according to the statement.
"Every operational plan rests on the assumption that nuclear deterrence is holding, and (ballistic missile submarines) like West Virginia are vital to a credible nuclear deterrence for the United States and our allies," STRATCOM commander Adm. Charles Richard said in the statement.
Russia's unprovoked invasion of Ukraine has caused many repercussions around the world, including soaring energy costs and increasing world famine, but it also indirectly strengthened the US military's ability to operate in the Indian Ocean.
The expanded ability of the US Navy to operate in the Indian Ocean has come about by the entrance of high-tech submarines from NATO allies into waters normally patrolled by the US Navy, and by likely new members of NATO -- Sweden and Finland -- adding their naval arsenals to the communal defence posture.
Arabian Sea's strategic importance
The West Virginia earlier in October surfaced in the Arabian Sea so that Gen. Michael "Erik" Kurilla, the commander of US Central Command (CENTCOM), could come aboard and participate in a communications exercise "to validate emerging and innovative tactics in the Indian Ocean", according to the Navy.
In the Indian Ocean, the Arabian Sea is becoming a strategically important region, and its features are ideal for the US Navy's Ohio-class nuclear-powered submarines.
The Arabian Sea has two important branches. The first runs from the Gulf of Aden in the southwest and the Red Sea through the strait of Bab al-Mandeb.
The second goes through the Gulf of Oman to the northwest, connecting with the Arabian Gulf.
With an area of almost 3.8 million square km and a maximum depth of 4,652 metres, the Arabian Sea provides an endless amount of safe patrolling areas and launch points for an Ohio-class submarine.
Its average depth of 2,734 metres makes it deeper than the Arabian Gulf, which itself is shallow in many places and generally seen as less suitable for large submarines.
The sea has unusually deep water near bordering lands, except in the northeast, off Pakistan and India, and few islands exist in the area.
The Arabian Sea is also recognised as one of the world's warmest seas, a property useful for submarines.
Its depth-temperature profile has an effect on the travel of sound waves and the effectiveness of sonar, a common technique used to detect subsurface vessels.
For example, active sonar, which detects submarines by sending out a pulse a sound and listening for echoes, is less effective.
In the sea's warm waters, the returning signal often gets lost.
The largest submarines ever built by the US Navy, the Ohio class includes 14 ballistic missile submarines (SSBNs) and four cruise missile submarines (SSGNs).
The SSBNs serve as an undetectable launch platform for intercontinental missiles, and are designed for stealth and the precise delivery of nuclear warheads, according to the Navy.
SSBNs are specifically made for extended deterrent patrols, and make up one leg of the US nuclear triad, which also includes land-based intercontinental ballistic missiles (ICBMs) and land-based long-range bombers.
The SSBNs' basic mission is to remain hidden at sea with their submarine-launched ballistic missiles (SLBMs) and deter a nuclear attack on the United States by another country by ensuring second-strike capability.
STRATCOM, whose mission is to deter strategic attack and employ forces to guarantee the security of the United States and its allies, controls the movements of these submarines, in addition to other land and air nuclear capabilities.
At any given moment, some of the Navy's Ohio-class submarines are conducting nuclear deterrent patrols.
According to data from last year, nine Ohio-class subs patrolled the Pacific Ocean, while five patrolled the Atlantic. The subs are homeported in the states of Georgia and Washington.
'Most destructive weapon'
The Ohio-class submarines are designed with three large-diameter logistics hatches that allow sailors to rapidly transfer supplies and equipment, cutting down on the time required for replenishment and maintenance.
They can operate for 15 or more years between major overhauls. On average, they spend 77 days at sea followed by 35 days of in-port for maintenance.
Each SSBN has two crews, Blue and Gold, which take turns manning the submarines.
"This maximises the SSBN's strategic availability, reduces the number of submarines required to meet strategic requirements, and allows for proper crew training, readiness and morale," according to the Navy.
The Ohio-class subs "may be the most destructive weapon system created by humankind", wrote Sebastien Roblin for the National Interest in 2021.
Each of the SSBNs originally carried up to 24 SLBMs with multiple, independently targeted warheads.
Under provisions of the New Strategic Arms Reduction Treaty, that number has been reduced to 20 missiles after each submarine had four of its missile tubes permanently deactivated.
The SSBN's strategic weapon is the Trident II D5 missile, "which can be fired from underwater to strike at targets more than 7,000 miles [11,265km] away depending on the load", Roblin wrote.
"As a Trident II re-enters the atmosphere at speeds of up to Mach 24, it splits into up to eight independent re-entry vehicles, each with a 100- or 475-kilotonne nuclear warhead."
A full salvo from an Ohio-class submarine can be launched in less than one minute, he noted.
"The current plan is to keep 12 Ohio-class subs active at a time with 20 Trident IIs each, while two more [SSBNs] remain in overhaul, keeping a total of 240 missiles active at a time with 1,090 warheads between them."