The Valentine Brothers' Ghoul Army

The Valentine Brothers' Ghoul Army was an army of Ghouls armed with military equipment (including but not exclusively limited to body armor, riot shields and military weaponry) that were used by Valentine Brothers to storm Hellsing HQ in the storylines of the original manga, the OVA and the anime series.

History
The Valentine Brothers were assigned the task of killing the entire Convention of Twelve, and destroying Hellsing HQ in the process. To this end, they were given command of a sizable number of armed and armored ghouls and a pair of travel lorries. Pretending at first to be lost tourists, they attacked Hellsing personnel at the compound's entrance and blasted the main driveway, allowing their forces to march into the complex.

Their brutal assault caught Hellsing forces by surprise, leaving most of them to be slain and devoured by the ghouls under the command of Jan Valentine. Despite putting up a brave resistance, it soon became obvious to the human defenders that they had little hope of overcoming the much larger and better-armed ghoul force. However, Jan's army encountered Walter C. Dornez and Seras Victoria in the hallway leading to the conference room, and they proved to be more than a match for the ghouls. Dornez's quick attacks with razor-sharp wires literally cut through many of Jan's minions, and the rest quickly died under fire from Seras's Harkonnen cannon. While the initial fighting force was effectively wiped out, they provided Jan with one final advantage; the Hellsing soldiers slaughtered by the ghouls had, in turn, become ghouls themselves.

Using Walter and Seras's shock as an opportunity, Jan managed to slip by the final defenders and make a run for the Convention of Twelve's conference room. Walter pursued the Millennium vampire, leaving Seras to fight the ghouls. Between her surprise at the reinforcements and their sheer numbers, the ghouls quickly managed to pin Seras down. Unfortunately for them, their attack caused the fledgling to briefly give into her bloodlust, engaging powers she had never used before to utterly rip the attackers to pieces. While she eventually snapped out of this fugue state, the former Hellsing personnel had been effectively neutralized. Integra Hellsing tried to have Walter dispose of the dying ghouls, but Sir Hugh Irons had her personally execute the dozens of ghouls with his revolver, dubbing it punishment for Integra's failure to mitigate the damage done by the assault.

Equipment
In all their incarnations, the Ghoul Army used a sizable force and were armed with machine guns or carbines, bulletproof armor to increase even more their odds of survival, and heavy anti-riot shields, always engraved with the message: "Boo Doo People Murder People" and the emblem of the Valentine Brothers, a stylized eye staring upwards with what appears to be a tear sliding down.

Trivia

 * Oddly, in the anime series, the eyes of the ghouls attacking Hellsing are normal, rather than the white irises of the other ghouls. This was corrected in the OVA, where they have the glowing purple eyes associated with ghouls.
 * The Ghouls made a brief appearance in some of the flashbacks in Hellsing: The Dawn anime.
 * The armored ghouls might not be ghouls created by the Valentine brothers, since Jan doesn't seem to have much knowledge about them or complete control over them. In the manga, he even asks Luke if they're trustworthy.
 * The Ghoul Army may have served as a prototype for the Letzte Bataillon as the Ghoul soldiers were the first result of the research done by the Doctor during Hellsing: The Dawn. Also, the attack lead by the Valentine Brothers was done to study the Hellsing Manor and its defense capabilities. This knowledge was used for the attack by Millennium forces led by Zorin Blitz although for not accounting for booby traps and the heavy artillery of Seras Victoria.