They have recently increased their U-boat activity.    From Wordnik.com.  [State of the Union Address (1790-2001)] Reference

At any rate, he went back to his U-boat and the undersea.    From Wordnik.com.  [The Sleuth of St. James's Square] Reference

On 17 September 1940 a German U-boat sank the City of Benares.    From Wordnik.com.  [Benares tragedy: 'All I can remember were the screams and cries for help'] Reference

I'd hold the submerged U-boat, 010, less than a thousand yards.    From Wordnik.com.  [CNN Transcript Apr 25, 2000] Reference

Monopole champagne went down off Finland, sunk by a German U-boat.    From Wordnik.com.  [Conventional Wisdom] Reference

U-boat, and I can't say to this day whether I struck or damaged her.    From Wordnik.com.  [Some Naval Yarns] Reference

At first, U-boat captains attempted to discriminate in their attacks.    From Wordnik.com.  [Castles of Steel]

The U-boat captain was filled with admiration for the British sailors.    From Wordnik.com.  [Castles of Steel]

Weddigen hurried up the ladder, took a look, and ordered the U-boat to dive.    From Wordnik.com.  [Castles of Steel]

Halifax citizens, described how the Olympic sank the U-boat 103, a few months ago.    From Wordnik.com.  [Punch, or the London Charivari, Volume 156, March 12, 1919] Reference

Expectations from a U-boat campaign against the British fleet were scarcely greater.    From Wordnik.com.  [Castles of Steel]

U-boat and air warfare can decide the war, but this will last from one to two years. '.    From Wordnik.com.  [Operation Sea Lion]

Off Nova Scotia, Canada, divers found a U-boat that came awfully close to Canada's coastline.    From Wordnik.com.  [CNN Transcript Jul 15, 2004] Reference

Her radioed information on the Home Fleet's position was promptly passed to the U-boat packs.    From Wordnik.com.  [Operation Sea Lion]

Weddigen struggled to regain ballast, succeeded, and took the U-boat down again to fifty feet.    From Wordnik.com.  [Castles of Steel]

Thrasher thereby entered history as the first U.S. citizen to be killed at sea by a German U-boat.    From Wordnik.com.  [Castles of Steel]

Should a U-boat spot Lusitania in the war zone, the liner would be flying a neutral American flag.    From Wordnik.com.  [Castles of Steel]

On January 30, a single U-boat, U-21, sank three merchant ships off Liverpool in a single afternoon.    From Wordnik.com.  [Castles of Steel]

By watching shipping closely they gather information, too, that is of value to the U-boat commanders.    From Wordnik.com.  [The Apartment Next Door] Reference

And in fact, the old S-boat and even the U-boat were submarines that were much simpler and much smaller.    From Wordnik.com.  [CNN Transcript Apr 25, 2000] Reference

Ten days later, as the convoy approached the English Channel, a U-boat was reported off the Isle of Wight.    From Wordnik.com.  [Castles of Steel]

Eighty-two-year-old Don Carcos (ph) has been blind in one eye ever since a U-boat torpedoed his ship in 1942.    From Wordnik.com.  [CNN Transcript Dec 16, 2006] Reference

The cruiser Berwick and two destroyers had been damaged by U-boat attacks as they left Rosyth in the early hours.    From Wordnik.com.  [Operation Sea Lion]

The results of this pioneering operation did little to vindicate the U-boat in the eyes of the German Naval Staff.    From Wordnik.com.  [Castles of Steel]

The cruiser had headed straight for the U-boat, while the destroyer was coming up behind it with even greater speed.    From Wordnik.com.  [The Brighton Boys in the Radio Service] Reference

On 17 September 1940, a passenger ship called the City of Benares was sunk by a German U-boat while crossing the Atlantic.    From Wordnik.com.  [Benares tragedy: 'All I can remember were the screams and cries for help'] Reference

Four of the destroyers began to take aboard survivors from the trawler, while the other four began to hunt for the U-boat.    From Wordnik.com.  [Castles of Steel]

When the U-boat crew got back to their base in France and discovered that the Benares's cargo had been children, they wept.    From Wordnik.com.  [Benares tragedy: 'All I can remember were the screams and cries for help'] Reference

According to a member of the Inventions Board, over two thousand solutions of the U-boat problem have already been received.    From Wordnik.com.  [Punch, or the London Charivari, Volume 152, May 23, 1917] Reference

Ultimately, U-boat warfare was refined into one or another of two basic operational strategies: restricted and unrestricted.    From Wordnik.com.  [Castles of Steel]

UB-116 was the only submarine destroyed by a shore-controlled minefield during the Great War, and the last U-boat sunk during that war.    From Wordnik.com.  [Castles of Steel]

The U-boat itself let loose a shot, and with such accuracy that only the sudden maneuver of the transport at that instant saved it from being hit.    From Wordnik.com.  [The Brighton Boys in the Radio Service] Reference

And the aim of her gunners was deadly! for just as the U-boat began to submerge, one of the big projectiles from the destroyer hit her squarely amidships.    From Wordnik.com.  [The Brighton Boys in the Radio Service] Reference