HMS Queen Elizabeth (QNLZ), procured by the UK Ministry of Defence (MoD) for the Royal Navy (RN) from the Aircraft Carrier Alliance (ACA), is the first aircraft carrier in the world to utilise an Integrated Full Electrical Power and Propulsion System (IFEP). While building on the design and lessons learned from the UK RN’s Type 45 Destroyer, the first front line warship to utilise IFEP, it also presented a step change in size and complexity, not only of the high voltage (HV) electrical power and propulsion (P&P) system and its automation control system, but also the ship’s wider distribution, control and auxiliary/ancillary systems, which both rely on and support the HV IFEP. Unlike its forerunner Type 45, QNLZ did not benefit from a full-scale shore-based test demonstrator with the cost/benefit decision being taken to carry the system integration and operational risk into the commissioning and trials phase of the project. The challenge presented to the ACA P&P Sub-Alliance (comprising Thales, GE Power Conversion, Rolls-Royce and L3) was therefore to develop a commissioning and trials strategy, programme and documentation set that would allow all elements of the IFEP to be set-to-work in as safe and efficient a manner as possible, with the goal of gaining acceptance from the MoD by delivering the required capability to the RN. This paper will present the methods adopted during this 10-year programme highlighting; 1. The processes followed to develop and then deliver a holistic integrated system commissioning strategy and plan. 2. The pull through and implementation of lessons learned and derisking from previous programmes. 3. The development of the detailed test and trials documentation to allow the P&P equipment and system to be commissioned, trialled and accepted allowing successful delivery into service. 4. The expected and unexpected challenges faced prior to and during the whole-system commissioning and trials phase and what was done to overcome these. 5. The planning and coordination of system integration and sea trials. 6. The lessons learned, successes and best practice that are being taken forward into the programme for HMS Prince of Wales (PWLS).