Late-war Sherman guns would penetrate any true ironclad

What is the strongest ironclad a 1945 Sherman tank platoon could sink or disable at a guarded choke point?

Any true ironclad would be vulnerable; late-war tank ammunition was built to defeat steel armor and would overwhelm earlier iron protection.

The scenario places an ironclad in a choke point exposed to direct tank fire. Late-war Sherman variants armed with the 76 mm gun or British 17-pounder fired projectiles designed for armor-grade steel rather than nineteenth-century iron plate. No completed true ironclad is judged capable of reliably withstanding the platoon. A ship would need later Harvey steel or comparable armor technology before the engagement became uncertain. The mismatch shows how rapidly projectile and armor metallurgy evolved.