Italy was teetering on the edge of defeat by the end of the summer of 1943. Sicily was lost, Mussolini had been deposed in late July, and the Allied invasion of mainland Italy was imminent. The Italian fleet was cooped up in La Spezia in Northern Italy slated to sail out on September 9 and attack the Allied fleet guarding the landings at Salerno.
 
Saving the Italian fleet
That mission never came about, as Italy secretly signed the Armistice of Cassibile the day before, changing sides. The fleet was now to head for Malta (The Siege of Malta) and surrender to the British there. The Germans had been expecting such a turn of events and moved rapidly, with Rommel (The Accomplishments and Legacy of the Desert Fox) and Kesselring (Kesselring – Part II) securing much of Italy and disarming or capturing Italian forces. It was obvious that the Germans wanted to either grab the Italian fleet or destroy it to prevent it from falling into Allied hands – very much like how the British attacked and sunk French ships in North Africa after the surrender of France to prevent the Third Reich from using them. The Italian fleet had to move quickly if it wanted to avoid either fate.
 
At first, the plan was for the fleet to depart La Spezia and head south to Rome, pick up Italian King Victor Emmanuel III, his court and his government, and transport them to La Maddalena, a town and naval base on the northern coast of the Italian island of Sardinia, just a few miles away from the French island of Corsica. (Mussolini himself was briefly held in a private villa at La Maddalena before being transported to the hotel in mainland Italy he would later be rescued from by the Germans (Rescuing Mussolini).) Once there, the king would form a new, pro-Allies government, while the fleet would be ordered to either Malta or the Allies-held North African seaport of Bône to surrender there.

Part of the plan quickly had to be scratched as the king fled Rome in another direction. The fleet was still ordered to sail to La Maddalena, heading southwest from Italy and circumnavigating Corsica from the west. As before, they would be given their final destination once in Sardinia.
 
The Roma’s last voyage
The fleet set sail on September 9. As the flagship, Roma had not only its own Captain Adone Del Cima on board, but also Admiral Carlo Bergamini, who was in overall command of the fleet. The core of the force was formed by the three Littorio-class battleships. (The lead ship of the class, the Littorio, had recently been renamed Italia for political reasons. “Littorio” is the modern Italian word for “Lictor,” a kind of attendant and bodyguard to magistrates in ancient Rome. Lictors carried the fasces, a bundle or rods with an axe in the middle. It was a symbol of power, and gave the name and much of the symbology of Mussolini’s Fascist Party. After the armistice, the Italian government was anxious to get rid of a ship name so closely tied to Fascism.) The battleships were escorted by three light cruisers, eight destroyers and several patrol vessels. Three more light cruisers sailing out of Genoa joined the fleet later.
 
At 1:40 pm, with the fleet already close to La Maddalena, they received a radio message that German forces had already captured the port. The fleet turned around and headed for Malta. At around 2 pm, the ships had exited the Strait of Bonifacio between Sardinia and Corsica; the Western Mediterranean lay before them.
 
Lookouts eventually noticed a flight of twin-engine aircraft following them from afar at high altitude. They could not be identified at that range, but Admiral Bergamini hoped it would be the Allied escort they were previously promised.

At 4:02 pm, a second bomb struck Roma, causing more crippling damage. Seconds later, one of the turrets flew clean off to the side, propelled by the detonation of the magazine underneath. Admiral Bergamini, his staff and Captain Del Lima were killed in the explosion. The ship quickly capsized due to catastrophic flooding and broke in two. According to an inquest at the time, 596 men survived and 1,253 went down. (More recent historical research suggests the numbers might have been 628 survivors 1,393 fatalities.) The rest of the battered Italian fleet turned south and eventually reached safety in Africa.

The murder weapon
But what was the mysterious bomb that seemed to steer itself? It was Germany’s newest experimental weapon. It was known by several names: Ruhrstahl SD 1400 X, Kramer X-1, PC 1400X, FX 1400, or its nickname, Fritz X. German forces fighting in the Spanish Civil War learned how hard it was to hit a maneuvering ship with a traditional bomb, and Germany started experimenting with radio-controlled bombs in 1938. Two designs were completed and ready for action by the late summer of 1943. The Henschel Hs 293 was a glide bomb attached to a jet engine. It already managed to sink a British sloop in late August, but it was a complex device and only suited for use against unarmored light warships and cargo vessels.
 
The Fritz X was simpler, more powerful and enjoyed far more success. It weighed 3,460 lb (1,570 kg) and carried 710 lb (320 kg) of explosives. The bomb had an aerodynamic nose, four fins, and a boxy, ring-shaped tail assemblage with several movable control surfaces. The control surfaces could be controlled (and thus the bomb steered) via radio waves by the bomber of the plane that dropped the warhead. A bright flare was attached to the bomb, and the plane carrying it had to “toss” it towards the target by climbing during release. Once it was away, all the bombardier had to do was look through his bomb sight and steer it so it remained lined up with the target until the moment of impact. Any one of 18 command frequencies could be used, making it much harder for the Allies to jam signals by flooding the air with radio waves. It usually hit while travelling at near supersonic speed, giving it enough punch to penetrate all the way through an armored ship and detonate under the keel.

The Fritz X in combat
The only unit to use the Fritz X operationally was Kampfgeschwader (“Combat Squadron”) 100, which flew medium and heavy bombers. The bomb was actually first dropped in late July over a port in Sicily, but no hits were made and the Allies did not realize they were facing a new type of weapon. The sinking of the Roma unleashed a brief period of terror. The American light cruiser USS Savannah was hit by a Fritz X on September 11 and had to retire to the U.S. for eight months of repair. Four of the Savannah’s sailors were trapped in a watertight compartment for 60 hours during the recovery effort. The Savannah’s sister ship USS Philadelphia had a near miss on the same day. The British light cruiser HMS Uganda was hit and crippled two days later, and the ship had to be towed to Malta. On September 16, a Fritz X caused heavy damaged (but surprisingly few casualties) to the British battleship HMS Warspite.
 
The Fritz X had two weak points, and the Allies were quick to exploit both. The bomber had to have a line of sight to the bomb during the entire attack, since he would not have known how to steer it otherwise. This meant that the plane dropping the bomb had to fly directly forward for a significant amount of time, which made it an easy target for interceptors in the air.

The other way to combat the guided bomb was to jam the radio signals, but as it was mentioned before, the jammer first needed to figure out which of the 18 frequencies was in use. In early 1944, a new British transmitter provided a solution to the problem. Due to various hardware limitations that still exist in modern radios, the bomb’s radio receiver used a so-called intermediate frequency: regardless of which of the 18 command frequencies were in use, the signal was always translated to the same specific frequency, 3 MHz, for a certain stage of the transmission process. The British Type 650 transmitter sidestepped the issue of picking the right frequency by simply jamming at 3 MHz, which attacked the intermediate frequency regardless of settings.  
 
Allied efforts
Naturally, the Allies were also developing their own guided bombs even. The American AZON guided bomb, most effective against long, narrow stationary targets like bridges and railways, was first deployed in 1944 and used a similar radio control system that forced the bombardier to maintain line of sight with the bomb. A variety of more advanced systems using radar or infrared guidance were also in development, but most of them arrived too late for service in World War II. (With the notable exception of the American ASM-N-2 Bat radar-guided glide bomb)