From Final Fantasy - Wiki on Neoseeker

Destroy the Mobile Artillery is a mission from Final Fantasy VII: Crisis Core. For a complete list, visit Missions (FFVII:CC).

Introduction

Mobile artillery produced to counter Genesis’s weapons has gone berserk due to careless QA testing. They have broken through the factory walls and are now heading toward the residential district. Destroy them before they reach the citizenry.

Enemies

• Bee Saucer III
• Martial Tank (boss battle)
• Sky Armor
• Support Machine+ (boss battle)

Chests

• X-Potion (north)

Strategy

Head around the bend and head north. Grab the X-Potion on the way to the boss. The Martial Tank will summon Support Machines. Destroy them quickly. They may be regenerated, but they are a nuisance and slow you down if you leave them in the field. Any Hell materia will help do a good amount of damage and allow you to keep your distance.