Last week, Russia launched a first-ever salvo of four intercontinental, nuclear capable submarine launched ballistic missile in under 15 seconds from a single submarine. Many pointed to this capability demonstration as more than just a test of their newest sub platform and accompanying missiles — they saw it as a demonstration of Russia’s growing emphasis on submersible naval warfare.

The same week, U.K. Defense Secretary Gavin Williamson spoke before a crowd at the Royal United Service Institute’s conference on sea warfare, offering a sobering glimpse into just how widespread Russian submarine and general naval activity has become in the waters around the United Kingdom.

“Look at Russia’s resurgence under President Putin. Its submarine activity has increased tenfold in the North Atlantic,” he said. “But that’s not all — in 2010 a Royal Navy ship was called on just once to respond to Russian Navy ships approaching UK territorial waters. Last year we had to respond 33 times.”

Williamson went on to assert that this dramatic uptick in Russian naval activity “goes to show the increasing aggression, increasing assertiveness of Russia.”