The SEA 5000 Phase 1 Project (Hunter Class Frigate Design and Construction) Integrated Master Schedule (IMS) integrates the BAE Systems Maritime Australia’s (BAESMA) Contract Master Schedule (CMS), made up of 26 schedules, with the Commonwealth of Australia (CoA) schedules which do not fall under BAESMA’s Hunter Class Frigate Program Head Contract. For example, while the delivery of a weapon system could be delivered by the CoA as Government Furnished Equipment (GFE), it is still critical to the successful delivery of the SEA5000-1 Project. A particular challenge with the development of the SEA5000-1 IMS is that BAESMA developed and maintained the CMS in Primavera P6 (P6), while the IMS is maintained by the CoA in Open Plan Professional (OPP). Differences in scheduling software between organisations can be a common integration issue amongst organisations participating in major Defence acquisition projects. This presentation highlights the challenges and lessons learned from developing the SEA5000-1 IMS including the: Tools and techniques used to the develop IMS, including the newly developed conversion tool that facilitates and maintains logic level integration between the P6 CMS into the OPP IMS. Benefits of working closely with and maintaining a productive working relationship with the SEA5000-1 Prime Contractor BAESMA.