The Type 23 Frigate (T23) has been extended in-service well beyond its initial design life of 18 years, with some ships due to be over 35 years old when they leave service. To ensure the vessels remain capable and provide the required availability demanded by the Royal Navy a T23 Life Extension (LIFEX) programme was set up to meet this revised end of life. A significant element of this LIFEX and the focus of this paper is PGMU (Power Generation and MCAS Update). This paper builds on other papers presented by my colleagues at previous conferences. This edition will cover issues that have arisen during the fit, lessons learnt that can be carried forward into future vessels and the test procedures of systems and equipment new to the Royal Navy. Challenges during fit have arisen from; • Limited space and access for the new equipment and systems • The inability to survey some spaces before the work commenced to confirm dimensions against original drawings • The provision of sufficient shock clearance during fit • The requirement to use modern off the shelf commercial equipment and yet also to conform to Defence Standards, which in some cases are out of date and written to old fashioned Admiralty Specifications • The physical integration of modern equipment and the re-designing of a legacy platform to new standards. PGMU comes at a very interesting time for the Royal Navy, with a similar project following closely behind; the Power Improvement Plan (PIP) for Type 45 Destroyer (T45). In addition to PGMU and PIP, very similar DG sets are also being fitted to the T26 Frigates. The occurrence of three RN platforms using modern DG sets from the same family marks a turning point for the Royal Navy, where it has moved firmly into the 21st century with regards to diesel electric power generation, and the changes in operating and maintenance procedures that this brings with it. Therefore, I will also touch on the challenges of Integrated Logistic Support at this stage of a project.