A new tactic adopted by Somali pirates based off the coast of Africa, designed to extend the range and mobility of their operations is causing concern among U.S. naval forces in the region.

In recent months, criminal gangs of privateers off the coast of Somalia have begun to use converted merchant ships as floating bases of operation, as a way to evade anti-piracy missions by U.S. and coalition naval forces, according to Vice Adm. Mark Fox, commander of U.S. Naval Forces Central Command, 5th Fleet.

“This is a serious issue,” he said this week during a Defense Writers Group breakfast in Washington. “We have adapted and the pirates have adapted.”

Fifth fleet first encountered these converted commercial sea liners last September off the Gulf of Aden, where a majority of pirate attacks in the region take place, Fox said. The three-star admiral assumed command of NAVCENT in mid-2010.

What they found was a ship filled with enough munitions and supplies to support up to eight “pirate action groups” almost 1,000 miles off the Somali coastline. From these ships, pirates can launch attacks against commercial vessels in relatively ungoverned seas.

On average, thousands of commercial vessels transport goods and materiel along those shipping transit routes in the gulf, he said. “We’re talking about [an area] from Newfoundland to Key West,” Fox said. “It is a pretty vast area…so when we are not there, they are capable of sometimes successful pirate attacks.”

Before the use of motherships, Somali pirates were only able to carry out attacks against merchant vessels during certain times of the year. The volatile monsoon seasons in the gulf would render the seas impassible for the small, outboard motor-powered boats pirates would use to board larger ships, according to Fox.

The smaller, underpowered boats would also limit pirate activity to coastline of Somalia and neighboring Yemen, he added. That said, commercial freighters could simply chart a course further from the Somali coastline and closer Indian shores to avoid attacks.

“Originally, pirate activity was based on the proximity to the land…[from] Somalia to Yemen, so we focused our attention and efforts on the Gulf of Aden…[and] you would see pirate activity focused on those times when small boats are able to go out to sea,” Fox said.

That focus by U.S. and coalition forces, he noted, has been able to drop the number of pirate attacks to between “only between one and two successful acts” in the gulf in a four-month period, he noted.

But the shifting tactics of the Somalis, particularly the use of mothership vessels, could put at risk the relative calm that has been brought to the region.

Running piracy missions from these floating bases of operation has essentially eliminated the annual lull in activity, allowing attacks to continue year-round while protecting pirate crews from the harsh maritime environment.

The use of motherships has also allowed pirates to carry out attack ships in deeper waters, and exponentially increase the time they patrol those waters, rendering the seek and avoid tactic used by commercial fleets null and void, the NAVCENT chief said.

In some instances, the intelligence, surveillance and reconnaissance assets used by NAVCENT to conduct anti-piracy operations are useless, due to the limited range of those platforms.

“These ships go out…at much greater distances with much longer persistence than we have seen,” Fox said. “So now [they are] 1,000 miles off the coast of Somalia…if I fly a P-3 out of Djibouti, he flies 1,300 nautical miles and comes back. That is his range. So they are going where we are not, where we do not have [a] persistent presence.”

Consequently, while the number of attacks has dwindled, the number of hostages taken by Somali pirates has grown, from 350 hostages taken to 750 in that same time span, Fox added.

While the mothership strategy has been in common use by drug cartels moving narcotics shipments from bases along the South America coastline to ports of entry in the United States, its presence within the shipping lanes of Western Africa is one Navy officials are struggling to cope with.

“They are adaptive, they are flexible, they are thinking. We are facing a thinking opponent here,” Fox said. “They know our redlines, they know our modes of operation…but the mothership, in my opinion, is potentially a game changer.”