Darpa awards contracts for underwater express

A high speed submarine will be designed with the aim of carrying out high-speed littoral missions using supercavitation technology, testing the feasibility of the technology to transport high-value cargo and/or small units of personnel at speeds up to 100 knots/hour. The notional US vehicle aims to operate covertly – if surface and acoustic signatures can be reduced enough – and manage speed while avoiding surface wave ‘slamming’ injuries. Proposal documents seen by Jane’s suggest that the demonstrator vehicle will improve upon the Shkval with a movable, retractable cavitator on its nose cone.

The drawbacks of supercavitation would be reduced if it can be made stealthier and with better directional control. The nature of the planned operations is also to enable faster coastal deployment of special forces.

Drawbacks as noted from wikipedia:
Naval combat frequently occurs over significant distances; the Mark 48 torpedo, the staple torpedo of the US navy, has a range of five miles with unconfirmed reports of ranges in excess of twenty miles. The maximum speed of at least 32 miles per hour, (unconfirmed reports indicate speeds upwards of 60 mph) meaning it can reach its maximum range in a matter of minutes (ten to twenty, depending on the figures used). A supercavitating torpedo traveling at 230mph would still take over a minute to reach a destination five miles away, and around six minutes to reach a target twenty miles away. This is more than ample time for a target to dodge. But whereas conventional torpedoes are capable of homing in on a target using either wires connected to the launching ship or active sonar, the nature of supercavitation precludes either method of guidance. The supercavitating engine would sever any wires attached to the torpedo, and the bubble of vapor surrounding the torpedo both enables it to travel at very high speeds and prevents the use of sonar. Supercavitation also produces an incredible amount of noise, which alerts the target to both the torpedo and the location of the launching sub. A common submarine tactic is to quietly launch a torpedo, but not to activate it until the firing sub has moved a few hundred yards away, then activating it and guiding it to the target. Supercavitating torpedoes are only capable of being “dumb-fired” directly from the launching vessel, which would immediately reveal its position, a lethal mistake in modern naval warfare. As the torpedoes produced by the American navy – and sold through arms contracts to allied navies – have incredible guidance systems, interest in supercavitation has been rather muted in the Western naval community.