Home News and Resources News News 06 May, 2026 Maritime Autonomous Surface Ships (MASS): Clarifying the IMO Definitions for Declarations Dean Crossley Head of Loss Prevention Asia As digitalisation continues to shape the maritime sector, increasing attention is being paid to Maritime Autonomous Surface Ships (MASS) and the terminology associated with them. This is now becoming evident in documentation and declarations, where Members may be asked to state a vessel’s “degree of autonomy”. Download PDF Recent cases have shown that as declarations are updated to reflect MASS, the inclusion of “degree of autonomy” is creating uncertainty for conventionally operated vessels. This is not unexpected, as the terminology stems from ongoing regulatory work by the International Maritime Organization (IMO) and is intended to address emerging MASS operating models rather than routine declarations for conventional ships. The IMO introduced the concept of “degrees of autonomy” as part of its Regulatory Scoping Exercise for MASS, the outcome of which is set out in MSC.1/Circ.1638 . These definitions were designed to support a structured review of how existing conventions, such as SOLAS and COLREG, would apply to ships operating at varying levels of autonomy. They were not intended to serve as a classification tool for conventional ships currently in service, nor do they have any mandatory status. Within this framework, the IMO refers to four degrees of autonomy. Degree 1 concerns ships with automated processes and decision support, where seafarers remain on board to operate and control shipboard systems and functions, with some operations potentially automated or unsupervised at times, but with seafarers ready to take control. Degree 2 refers to remotely controlled ships with seafarers on board, while Degree 3 applies to remotely controlled ships without seafarers on board. Degree 4 refers to fully autonomous ships capable of making decisions and taking actions independently. At pre