"攻城用仰冲车" can be translated into English as "siege ladders (or battering rams with an upward-thrusting mechanism, depending on the specific design and historical context) used for storming a city."
However, a more precise and commonly accepted term in English for such siege engines, especially if they are designed to attack upwards (like a battering ram that can strike from a lower to a higher position or a siege ladder with a mechanism to help lift it against walls), might be described in more detail based on their function. If it specifically refers to a type of battering ram that has an upward-thrusting capability, a possible translation could be "upward-thrusting battering ram for siege warfare."
For simplicity and if the exact type isn't crucial, "siege ladders" or "battering rams for storming cities" could be used, keeping in mind that the exact translation may vary slightly based on the historical and technical specifics of the device in question.
A more concise and likely accurate translation, assuming it's a type of battering ram designed for upward strikes, would be:
"Upward-thrusting battering ram for siege attacks."