Swatting the Russian Moskito
Supposedly the very latest missile systems may be able to launch an interceptor rocket, accelerate it to the necessary Mach 4+ speeds very fast, and so manage to knock down such menaces as the Klub or Moskit ("mosquito"): but there's a lot of doubt about whether this would actually work - and there's no doubt at all about the crippling cost of such defensive kit and the limited number of counter-missiles a ship can fire before its tubes are empty.
But, as General Atomics has previously noted:
In the case of ship defense, the launch package can reach the horizon in seconds. This allows for engagement of threats much quicker and farther away than current systems, having the ability to replace multiple systems in the current layered defense approach, with the potential for reduction in the cost to defeat multiple threats by several orders of magnitude, and with a much deeper magazine than alternative approaches.
Certainly a railgun slug from the Blitzer, accelerating down the rails at 60,000G, is travelling at Mach 5 far sooner than an Aster can reach its top speed of Mach 4.5. The projectile could reach out and touch an inbound Vampire** much more quickly: a Blitzer-derived weapon would probably get more chances to score a hit than the Royal Navy's PAAMS/Sea Viper or the USN's Aegis warships would, and would have many more rounds to shoot. Asters and SM-2s have the advantage of being guided and more likely to make a hit, but the Blitzer's projectiles are already finned - it would be comparatively easy to make them smart, though the railgun would need to be aimed reasonably accurately to begin with.
In the nearish future, depending how accurate GA's "tactically relevant" puffery turns out to be, warships equipped with Blitzer-type railgun turrets might offer far better air defences than Type 45 or Aegis vessels can today. Such defences might only be penetrable by bigger, heavier railguns firing from beyond the horizon - along the lines of the Dahlgren boffins' desired 64-megajoule weapon. It would, of course, require a massive capital ship to carry such guns and power them for any serious rate of fire - such a future might see the big-gun (railgun) dreadnought battleship return to its lost dominion over the seas, ousting the parvenu aircraft carrier, missile cruiser etc.
General Atomics may not be the firm building the weapons, however. The US Office of Naval Research, in charge of the railgun effort, has previously commissioned GA for a lot of the work - indeed the Blitzer was developed for the ONR. However the next ONR railgun, expected to open fire at Dahlgren next year, is to be built by the North American acquisitions of BAE Systems plc. ®
*The Google cache at the time of writing confirms that it wasn't up as of the 12th, certainly. As you can imagine, we here on the Reg crazy weapons desk check General Atomics' press page daily.
**The NATO brevity code word for "hostile anti-ship missile", which would take a bit too long to say on a voice circuit during an air attack.