The Hellsing ARMS Anti-Tank Cannon 'Harkonnen', often referred to as simply "The Harkonnen", is the preferred firearm of Seras Victoria for much of the Hellsing series. She is the only one who uses it, and is probably one of the few who can because of its weight; Seras' sharp precision and superhuman strength are ideal for using it. The Harkonnen is stated by Walter to have enough firepower to destroy nearly anything other than a main battle tank, as well as being superior to the majority of military weapons.
Weighing 120 lb. (approx. 60 kg) unloaded, the 30 mm, single-shot breech loader cannon uses various types of shells, including depleted uranium with silver for piercing armored targets and incendiary napalm rounds for destroying large groups of opponents both on land and in the air. Carrying this weapon, the vampirically-enhanced Seras serves perfectly as long-range fire support. Her immense strength also allows her to use the weapon while moving; sometimes, especially in the manga, she wields it with an extraordinary ease, even firing over her shoulder.
Walter presents her with the Harkonnen as a weapon for her personal use in Volume 2.
- Before gaining the Harkonnen, Seras used a relatively smaller rifle, firing 13.7mm rounds, as is seen written on the gun in the OVA. In the manga this gun is unnamed but the letters BAERLKS are spelled out on its side; in the OVA, however, the gun has Harkonnen written in the same place.
- The size of the Harkonnen can be worked out by referencing the scene where it is first introduced by Walter, who stands it up next to himself. Walter's height is given as 191 cm, thus the Harkonnen can be worked out to be approximately 237 cm long, comparable to similar-caliber anti-tank guns.
- The Harkonnen's large size sometimes makes it hard to transport, a feature wryly remarked upon by Seras. Nevertheless, it continues to be her preferred weapon until it is destroyed.
- Seras' signature weapons are named after the main antagonist of Frank Herbert's novel Dune, Baron Vladimir Harkonnen. In Hellsing Ultimate Episode 7 (around 11:30 minutes) the name "Vladimir Harkonnen" can be read engraved on the weapon. And there is an appearance of the gun's "spirit" during dream sequences in the manga (and thus OVA) and episode previews in the anime; the spirit in question bears a strong resemblance to Baron Harkonnen from David Lynch's film adaptation of the novel.