When is a missile launcher no longer vertical?

At what angle does a VLS tube stop being a VLS tube?

Once it is no longer vertical to the keel and hull structure, it is an angled box launcher rather than a VLS cell.

The response defines a vertical launcher relative to the ship's keel and structural plane, not to the horizon while the hull rolls. A cell perpendicular to that reference can be supported symmetrically and can route exhaust through an arrangement designed around its vertical load. Once the launcher is deliberately canted, the ship must handle off-axis weight, launch momentum, and gas flow. Naval architects therefore treat the installation as a box or angled launcher rather than as a slightly imperfect VLS. Ordinary ship motion does not change the classification because the launcher and hull move together.