Most of today's definitions of LOA for MASS look at where human control resides (remote or onboard) and some form of graduated control capability for the automation system, e.g. ranging from decision support, human approval or vetoing of automated actions, to full automation. MASS has some characteristic factors that make the use of these LOAs difficult: 1. Ships are costly assets and are expected to always operate under human supervision.  2. MASS operations may last for several days or weeks, and for most of the time relatively little attention is needed from operators. 3. Ships move relatively slowly, and dangerous situations develop over time. This means that it may be possible for automation to warn the operator well before intervention is needed. Thus, in most cases we are looking at limited autonomy for the MASS, where a human operator can assist automation when necessary. To ensure an acceptable risk level for MASS the following issues are central: 1. It is necessary to define the operational limitations of the complete MASS system and automation. This defines the conditions when humans need to take control. 2. One must design the system so that it is clear what party is in control at any point in time, automation or human.  3. One must include facilities in the automation system to give an alarm to the human before intervention is necessary. 4. One must define the hand-over processes between automation and human so that both parties always know who is in control.This is a situation where "constrained autonomy" fully controls the ship under certain conditions and where a human takes over control when necessary. While there is a cooperation between human and automation, only one will be in control at any given point in time.