The aircraft manufacturers AB Förenade Flygverkstäder (AFF), AB Svenska Järnvägsverkstädernas Aeroplanavdelning (ASJA), Svenska Aeroplan AB (SAAB), Kockums Flygindustri and AB Götaverken (GV) were seen as likely competitors, but only ASJA, SAAB and GV responded.
The GV entry, GP 8, a Dornier Do 17 look-alike seemed best, but also most expensive. The chief designer Bo Lundberg left GV, which had decided to abandon its aircraft business, and started AB Svenska Flygplansverken (AFV) and had a mockup of the GP 8 accepted conditionally. In the mean time ASJA was merged with SAAB and SAAB given a contract with the air force.
With the outbreak of the war in 1939, it was decided to concentrate all work on Saab B 17, so B 18 was put on the back burner.
At first it was planned to use Bristol Taurus engines, but when British engines couldn't be gotten, it was decided to use a Swedish made Pratt & Whitney Twin Wasp, STWC-3, instead. The preferred engine however, was the DB605, but the figher J 21 got priority on them, so the first B 18's could not be equipped with them.
The fuselage was all metal with fabric covered control surfaces. For the first time in Sweden, the armour was an integral part of the structure. The canopy for the pilot and radio operator/gunner was offset to the left. A observer/bombardier/gunner had his place in the glazed nose.
Fixed armament consisted of three 13.2 mm guns, each with 300 rounds, one fixed forward firing in the starboard side of the fuselage controlled by the pilot, one rearward firing for the radio operator and one rearward firing in the lower fuselage for the bombardier.
The tactics for them, like for our Ju 86s, were level bombing attacks performed by a squadron of nine aircraft in three groups of three.
Internal bomb load was either two 500 kg or three 250 kg or ten 50 kg bombs. Under the wings could either eight 50 kg bombs or illumination flares be carried.
During 1946-47 all were converted into S 18As.
They were fitted with one vertical camera and one oblique in the nose. For night photography they were later fitted with one more camera and fitted for photo flash bombs under the wings.
In 1949 they were fitted with surplus US Navy radar sets, AN/APS-4 with Swedish designation PS-18/A, in pods under the nose.
As pure photo reconnaissance, they were soon replaced by Spitfires and Tunnans, but as maritime reconnaissance aircraft they continued in service until 1959 when they were replaced by S 32C Lansen.
As these aircraft were faster, tactics changed: Normal attack formation became eight aircraft squadrons, consisting of two groups of four, consisting of two pairs. Approach to the target was performed either with the whole squadron or groups, but the attack itself by pairs.
Level bomb runs were replaced by dive attacks, which were more effective, partly thanks to the dive bomb sight (m/42) developed by Erik Wilkenson at Saab. After locking on to the target, the sight computed release depending on speed, angle, wind and other factors. It was first used on B 17, later on A 32A and also exported.
Due to the new tactics, crew was reduced to two: Pilot and radio operator/navigator.
At the end of the 1940's, ground attack rockets were introduced in the air force. They were mounted under the outer wings (four heavy under each) and under the nose (four heavy).
The last ones were retired in 1958.
It had a more aerodynamic nose section since it from the beginning wasn't intended to have the lower gun, and thus faster. Otherwise it was structurally identical.
In addition to the bombs and rockets carried by B 18B, it was also intended to be able to carry a 1000 kg mine or 950 kg torpedo internally. The torpedo trials weren't successful, so the main armament for anti-ship attacks were rockets, two 20 mm guns in the lower nose and a 57 mm Bofors m/47 L/50 gun which could be mounted in the bomb bay in about two hours, with the muzzle protruding through a hatch in the lower nose. It weighed 735 kg and a total length of 5.3m Magazine capacity was 40 rounds plus one in the chamber. Reloading in the air wasn't possible. Firing rate was 3 rds/s and the maximum practical range for the 2.5 kg HE or AP projectiles was 2000 m. It had a well working recoil damper so in spite of the high recoil force (6 tons) flying properties weren't affected much. Reloading was by pneumatics, firing electric.
Trial armament was two 40 mm guns under the nose, but test firing shattered the nose glazing. The anti-ship missile Rb 302 was also trialled but didn't enter service. The descendant Rb 304/Rb 04 entered service on Lansen and Viggen.
The last ones were retired in 1958 after having been replaced by A 32A Lansen.
Rockets were taken out of use in 1952.
Bombing runs were made at a dive angle of 30-45 degrees starting from 1500 m altitude.
Gun attacks were made at dive angles of 10-20 degrees starting at 700 m. Thus they could be made with lower cloud bases and the attacking aircraft spent significantly shorter times over minimum which meant defending AAA had less time to engage.
Normally at least a squadron, eight aircraft, attacked simultaneously, but sometimes two or three squadrons attacked the same target almost simultaneously, from different directions (even contra course where those who just had dropped their bombs flew away from the target under those who were dropping their bombs).
As fighter performance improved the B 18/T 18s had to fly lower, in worse weather, at night and larger units.
All versions
Span 17 m
Length 13 m
Wing area 44 m2
Fuel load 1700 litres
B 18A B 18B T 18B
Engines STWC-3 DB 605B DB 605B
1065 hp 1475 hp 1475 hp
Empty weight 5550 kg 6100 kg 6100 kg
Max weight 8200 kg 8800 kg 9272 kg
Warload 1400 kg 1400 kg 1400 kg
Max altitude 8000 m 9800 m 9300 m
Max speed 465 km/h 570 km/h 600 km/h
Range 2200 km 2600 km 2600 km