The Bf 110's main strength was its ability to mount unusually powerful air-to-air weaponry. Early versions had four 7.92 mm MG 17 machine guns in the upper nose and two 20 mm MG FF/M cannons fitted in the lower part of the nose. Later versions replaced the MG FF/M with the more powerful 20 mm MG 151/20 cannons and many G-series aircraft, especially those which served in the bomber-destroyer role, had two 30 mm MK 108 cannons fitted instead of the MG 17. The defensive armament initially consisted of a single, flexibly mounted 7.92 mm MG 15 machine gun. Late F-series and prototype G-series were upgraded to a 7.92 mm MG 81 machine gun with a higher rate of fire, and the G-series was equipped with the twin-barreled MG 81Z. Many G-series night fighters were retrofitted or factory-built with the Schräge Musik off-bore gun system, which fired upward at an oblique angle for shooting down bombers while passing underneath; it was frequently equipped with two 20 mm MG FF/M, but field installations of the 20 mm MG 151/20 or 30 mm (1.18 in) MK 108 cannons were also used. The Schräge Musik weapons were typically mounted immediately in front of the rear cockpit.

The Bf 110 G-2/R1 was also capable of employing armament such as the Bordkanone series 37 mm (1.46 in) BK 3,7 autofed cannon, mounted in a conformal ventral gun pod under the fuselage. A single hit from this weapon was usually enough to destroy any Allied bomber.

The initial Bf 110 C-1/B fighter-bomber could carry two 250 kg (551 lb), two 500 kg (1,102 lb), or two 1,000 kg (2,204 lb) bombs on two ETC 500 racks under the fuselage and, starting with the Bf 110 E-0, could be supplemented by four additional 50 kg (110 lb) bombs on ETC 50 racks under the wing.

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - BF 110