Battlefield 4 Naval Strike was planned to come out March 25 but it seems that EA and DICE delayed the PC version of the third BF 4 expansion, according to the Battlefield Blog:

However, we are delaying the launch of Battlefield 4 Naval Strike on PC. We’ve detected an issue and it needs to be solved. Quality is our number one priority and we will not release Battlefield 4 Naval Strike on PC until we feel it meets the highest quality level possible. Once we have a confirmed date for PC, we’ll be sure to update those players on our official channels. We appreciate your patience and look forward to seeing everyone on the Battlefield.

The Battlefield 4 misery does not find an end. But it´s not too bad that they spare us to play an expansion with issues, while it is questionable if the delay will mean that we will see an expansion without issues, considering that the main game is not even fixed yet.