The US Navy seeks solutions to replace four disparate tube-type VLF high-power transmission systems used by the Fixed Submarine Broadcast System. The required solution must support 24/7 global operations from existing sites using existing waveforms and be implemented with minimal site downtime. Vendors must submit Phase 1 Solution Briefs, which are strongly recommended not to exceed five written pages or fifteen briefing slides. Submissions must be made via the specified PIEE Solicitation module link, as emailed submissions will not be accepted.