The problem of effectively supporting human operators as they model missions, supervise their plans, and observe execution, combines several open questions in human-aware planning. These include how to provide support during the mission modelling and specification phase, and how to provide effective assistance during the planning phase. In this paper, we present ongoing work to create a tool for human operators, which aims to support effective interactions and improve operator understanding and awareness throughout autonomous underwater vehicle missions. We present an architecture which incorporates modelling assistance, plan generation, explanation, and plan space exploration. Our approach starts with a task-bot interface that provides modelling assistance during the mission specification step and comprehensible plan explanations during planning, while supporting the operator in exploring the plan space. In addition, we present an example walkthrough to showcase the human-machine interaction and explanation representations.