The main plot focuses on two Royal Naval Volunteer Reserve Sub-Lieutenants, Lockhart and Ferraby, although the novel portrays point of view of a number of other crew members, including Commander Ericson, Lieutenant Morell, Chief Engine Room Artificer Watts and Petty Officer Tallow. The crew of the corvette HMS Compass Rose are subjected to all of the discomfort, boredom, and occasional horror of the Battle of the Atlantic. The plot comes to a head when Compass Rose is torpedoed by a German U-boat, and the survivors are reassigned to the River-class frigate Saltash. They survive the war having sunk a single U-Boat in five years of nearly continuous combat.
The novel was adapted into an Ealing Studios film in 1953, starring Jack Hawkins and Donald Sinden.
In 2003, The Cruel Sea was placed 113th in The BBC Big Read's Top 200 Books.
This novel and film provides examples of:
- Anyone Can Die: There's a war on, so yes. This goes for civilians as well as sailors.
- Artistic License Ships: Averted in the book, but zig-zagged in the film. The Compass Rose is portrayed by the Real Life Flower-class corvette HMS Coreopsis,note and the River-class Saltash is changed to the Castle-class Saltash Castle, as the film-makers couldn't get a hold of an actual River-class frigate. The German U-boats encountered in the film, however are played by a Royal Navy S-class submarine.note
- Attack Pattern Alpha: In the film, the crew refer to "pattern Baker" when adjusting the settings for the depth-charges during attacks on U-boats.
- Author Avatar: Lockhart in the book. Like him, Montsarrat was a journalist-turned RNVR officer who ended up as a First Lieutenant.
- Be Careful What You Wish For: In the book, Sub-Lieutenant Baker is desperate to lose his virginity. He ends up going to a prostitute — and catching a sexually-transmitted infection. His fear of having to live with this renders him indifferent to the prospect of death when Compass Rose sinks.
- Decoy Protagonist: Ferraby to an extent — he joins at the same time and with the same rank as Lockhart, but he ends up being a relatively minor character.
- Drowning My Sorrows:
- Ericson does this to cope with the guilt of attacking a U-boat that appeared to be positioned under British sailors in the water, increased by the inconclusive nature of the engagement, ending with the sonar contact being lost but no debris seen.
- Also Lockhart, after the death of his pregnant love interest Julie Hallam, lost at sea - about the worst death Lockhart can picture, although no details are given.
- Ensign Newbie: Ferraby and Lockhart. Lockhart gets better rather faster than Ferraby does.
- Face Death with Dignity: In the book, played straight by Tallow, Wainwright and Wells and averted by Watts, Gregg and Carslake when Compass Rose sinks.
- Fluffy the Terrible: The Flower-class corvettes were all named for kinds of flowers. It is specifically mentioned that the Navy had made sure "Pansy" was not on the list. Truth in Television, as HMS Heartsease was originally intended to be called HMS Pansy, but had its name changed before being launched.
- Averted, in that a "compass rose" is not a flower at all; its the design appearing on the face of a compass. The author stated in a later interview that this was deliberately done so that no actual vessel would be implied or inferred.
- Foregone Conclusion: We are told on the first page that Compass Rose will sink and be replaced.
- Heterosexual Life-Partners: Ericson and Lockhart, to the extent that Lockhart passes up the chance of commanding his own ship after the sinking of Compass Rose, in order to remain as Ericson's second-in-command.
- Miles Gloriosus: First Lieutenant Bennett in the book. After doing little more than bullying his subordinates, and shirking as many duties as he can, he is invalided off Compass Rose with a duodenal ulcer (which is implied to be faked) A conversation with another Australian officer reveals that he went on a speaking tour of his home country where he claimed to have commanded the ship single handed after Ericson was injured in battle.
- National Stereotypes: Played Straight in various forms. The only German character is a fanatical Nazi U-boat Captain in his twenties. The Dutch and Norwegians are dour and occasionally, belligerent; some Swedish officers appear as comic drunks. The French are distrusted and reckoned to lack backbone. The Irish get a very bad press.
- The Neidermeyer: Bennett, a lazy bully. He bullies Ferraby in particular, because Bennett thinks it's fun.
- Number Two: The story covers a "Number One's" duties (on anti-submarine craft) in exhaustive detail, since the protagonist is one (and the writer WAS one).
- Trial by Friendly Fire: The ship finds men in the water after their ship has been sunk by a U-boat. If the ship rescues the men, the U-boat will get away, and sink more ships. If they start dropping depth charges NOW, then the survivors will die, but there is a chance of sinking the sub. They drop the charges.
- Wacky Americans Have Wacky Names: The book mentions the appearance (pre-American entry) of "strange-looking destroyers, with long names often beginning with 'Jacob' or 'Ephraim'". American Destroyers were and are named for Naval officers, heroic sailors, and Secretaries of the Navy; British Destroyers for abstract adjectives and nouns (usually with some sort of "theme", or in some classes simple alliteration) and of course the "Flower" class Corvettes were named for Exactly What It Says on the Tin.