The B-17F Lucky Lass, part of the United States Army Air Forces (USAAF) 99th Bombardment Group (Heavy) (the "Diamondbacks") from the 12th Air Force is stationed at Navrin, Algeria in 1943. During a raid on Gerbini, Italy, with her Irish-American crew, the Lucky Lass is heavily damaged and the (pilot "Pops" (Jamie Martz), and both waist gunners, Jake (Anthony Ocasio) and Joe (Steve Holm) are killed.
Five days later, replacements arrive in the form of Co-pilot Michael Schmidt (Bug Hall) and two new waist gunners: Tom (Jeremy Ray Valdez) and Oliver (Tony Elias). On their walk-around of the North African base, the replacements are introduced to the alcohol still flight engineer Burt (Chris Owen) has put together from bomber parts, to make moonshine from the ethanol blended aviation fuel. With new crew members now available, crew chief Caparelli (Howard Gibson) is pressured to clear their aircraft to fly (which he does). The crew throws a party to celebrate, where they find out Michael does not drink, upsetting everybody but Wally (Donnie Jeffcoat), now the pilot and aircraft commander), who gives the new young pilot advice on fitting in with the tightly-knit crew.
During the next mission, Wally gets ptomaine poisoning from a local delicacy, spiced goat meat, and asks Michael to take the controls on the flight. Although watching his instruments, Michael ends up getting lost and under attack by Luftwaffe Messerschmitt Bf 109G fighters, only surviving after the intervention of USAAF Curtiss P-40F Warhawk fighters. The Lucky Lass is forced to abort and land at their base. That night, there is a fierce sandstorm forcing everyone on the base to stay inside. Burt starts up his still to make alcohol for their inevitable late-night party, but accidentally leaves a tap open, leaking alcohol.
When the engines are not responsive, the aircraft is forced to abort yet another "milk run" (an easy mission) to Messina, Sicily. The crew blames Michael, considering him a jinx. Uncharacteristically, he starts drinking. On their return to base, Burt's still explodes, ending his illicit enterprise. Caparelli says there's nothing "mechanically" wrong with their B-17 but, meanwhile, the aircraft that continued on mission begin to arrive back, with signs of heavy damage, indicating that it had not been an easy mission. Wally assures Michael that by aborting the mission, he had perhaps saved lives.
With the Lucky Lass grounded, the crew is mixed into other crews for the next mission, but Charlie (Manu Intiraymi), Eddie (Joseph Williamson) and Michael are not assigned. Offering to help in stripping the engines, Michael convinces Caparelli to discover the "gremlins" that brought down the aircraft. Sand is found in the engine's oil pumps. Meanwhile, to make good on a promise to Al (Tim Hade) for a celebration on his safe return, and with no alcohol left, Charlie is caught stealing liquor from the officer's club and is facing a court-martial. Eddie pleads with Michael to intervene with Col Shay (John Laughlin), the "Old Man". Michael intervenes, facing down fearsome quartermaster Monroe (Matt Biedel) and claims he asked Charlie to get alcohol to help clean the engine filters. Charlie further says Scotch whiskey was needed as the Lass is an Irish bomber. The base commander pretends to believe the story. The whole crew celebrate Charlie's vindication, and declare Michael an honorary Irishman, christening him, "O'Schmidt".
July 19 arrives and Lucky Lass is cleared to fly the Rome mission. On the run in to the target, encountering heavy anti-aircraft fire, Burt suffers a head wound, but they manage to drop their bombs on the target. However, as they make the turn home, a B-17 flying above them is hit and begins falling in their direction. They climb, but the doomed bomber's wing breaks of part of their right horizontal stabilizer, causing them to go into an uncontrolled climb until they stall and enter a spin.
At the last second, Michael and Wally manage to pull up, but they are now very low over Rome and taking heavy fire from ground fire. Losing an engine, and taking hits, Wally and Tom are killed while other crew members are wounded. Michael asks Archie (Sean McGowan) to come to the cockpit to help him fly, since the navigator was once in flight school. Even though Archie is wounded, he comes to help. The Lucky Lass gets away from Rome, and makes a run for a British airbase at Malta.
Michael asks Al from his position as the ball turret gunner about their situation, who reports that aside from the knocked-out engines and other damage, the B-17 appears to be fine. When lowering the landing gear, however, the port gear falls away, forcing Michael to order the last able-bodied men to bail out while he and Archie will try to land at the RAF base.
As Michael helps the crew, Archie coughs up blood. Michael then tries to calm him down, nonetheless, Archie's parachute had been destroyed. Michael says that they can land the aircraft on the water or both jump using his parachute, which Archie agrees to, but he then tells him to "take care of the boys" and pushes Michael out. Archie then takes control of the B-17 and starts climbing, but in its damaged state, it cannot take the stress and disintegrates, taking the navigator with it.
Some time later, back at Narvin, a new replacement checks in with Michael, now the flight commander of a new bomber, starting the cycle again.
In the closing credits, Fortress filmmakers make the sardonic declaration, "No B-17s were hurt in the making of this film." The statement was accurate as the low budget feature could not afford to use actual surviving B-17s, either in private collections or in museums. With principal photography undertaken in 2011, Radical 3D was responsible for the authentic computer-generated imagery (CGI) film effects. The company's involvement with Lucasfilm, Fox Television, IMAX, Warner Brothers and Disney was in feature work, including the similar productions, George Lucas’s Red Tails (2012) and the Tom Hanks production of Beyond All Boundaries (2009) (for which effects have been nominated for a VES award).
Radical 3D was also involved in television projects for Discovery Channel, History Channel and National Geographic Channel including 24 and Dogfights (premiered in 2006), the highest rated series on the History Channel during its first season.
For Fortress, a full-scale interior mock-up was made, recreating the fuselage from tail to cockpit. The principal exterior visual effects began with a CGI rendition that had a unique origin. The producers acquired a 1:28 scale Guillow’s B-17 Balsa wood "flying" model and scaled it up, producing, in effect, a 1:1 B-17 scale model. The upper fuselage, above the “side keels” was placed on a wooden ladder frame, which rested, in turn, on scrap tires. Manipulating the setup, the fuselage was jostled to simulate turbulence and make the actors react to the motion of the aircraft.
Location photography for the Algerian scenes in Fortress took place at Rocking Horse Ranch, Ramona, California in 2011. Other studio work was completed at Radical 3D facilities in Culver City, California.
Fortress depicted accurately the bombing of Rome in World War II in 1943, primarily by Allied aircraft, before the city was freed by the Allies on June 4, 1944. Pope Pius XII was initially unsuccessful in attempting to have Rome declared an open city, although negotiations took place with President Roosevelt via Cardinal Francis Spellman.
The first Allied bombardment occurred on July 19, 1943 and was carried out by 500 American bombers (a mix of B-17 and B-24 bombers). A total of 1,168 tons of bombs resulted in the entire working class district of San Lorenzo being destroyed with 3,000 Italian civilians killed in the raids over five residential/railway districts. The military targets were few, the largest Stazione Termini contained a marshalling yard, railways and industries that manufactured steel, textile products and glass. In the 110,000 sorties that comprised the Allied Rome air campaign, 600 aircraft were lost and 3,600 air crew members died; 60,000 tons of bombs were dropped in the 78 days before Rome was captured.
The producers gave "very special thanks" to the Planes of Fame Air Museum, Chino, California and also credited 21 technical advisors including staff at the Yanks Air Museum, also in Chino.
Due to its direct-to-video release, Fortress was not critically reviewed, however, Danny Shamon reviewed the video in 2011, identifying the film elements that were effective, "For a low budget film I thought the aerial combat and filming were fantastic. I liked the sets, and it is obvious that some time was taken on the outfits, and items used during this time period.". Reviewer Ray Nyland noted: " 'Fortress is a low budget film that delivers. The air action sequences are loud, frenetic and exciting with some genuine heart in mouth moments. The camera shakes as the B-17 ploughs through heavy flak, and German fighters flash and spin past, all the time accompanied by explosions and machinegun fire that resonates around the speakers. Most of the model and CGI work of the air battles are neatly done, and believable ..."
In TV Tropes, Fortress was characterized as: "Despite a shoestring production budget that made for lots of conspicuous CGI, the movie was very well-researched and well-executed."