The Joint European Torus (JET) has recently begun a series of experiments with deuterium-tritium plasmas (DTE1). These are the first plasma experiments with a 50:50 D-T mixture in a Tokamak with a Divertor. The extensive technical work to ensure that the JET machine and its major subsystems were able to carry out an extended period of D-T operation is described. This includes the JET Active Gas Handling System (AGHS) and its commissioning to full closed-cycle operation. The AGHS has supplied around 40g of tritium to the JET Torus and Neutral Beam Injectors (NBI) and has reprocessed batches of tritium of over 11g returned from the cryopumps of the Torus and NBI. The modifications to bring the NBI system to full tritium compatibility and its commissioning are described. The injection of tritium beams at up to 155kV energy and up to total powers of 11.3MW has taken place. JET had to be subjected to extensive deterministic analyses of Design Basis Accidents (DBAs) to establish changes required to protection systems for D-T operation and to satisfy the regulatory authorities. An example of the practical consequences of these analyses and a discussion of the methodology is included. The history of a successful plant intervention to repair a small water leak in the Tritium Neutral Injector is discussed. The success of the Exhaust Detritiation System (EDS) in keeping environmental discharges to below management limits in this exercise, and the lessons learnt generally, are also presented.