A ship or submarine has a number of signatures - active and passive acoustic, pressure, wake, static electric (UEP), static magnetic, extreme low-frequency electromagnetic (ELFE) - and other signatures like internal waves and changed biological activity and spillage. The rapid development of intelligent sensor systems, with data fusion capability, coupled with demands to participate in international operations, gives rise to new requirements for stealth and signature reduction for future systems, tactics and weapon platforms. Experimental as well as theoretical studies are performed within the project Underwater signatures. Acoustical, hydrodynamical as well as electromagnetic signatures are considered for ships and submarines. The studies are focused upon (i) fundamental mechanisms and principles for passively and actively generated underwater signatures, (ii) environmental effects upon signal generation and propagation, (iii) coupling between signatures of different types in connection with generation and reduction of signatures. Particular emphasis is given to prospects of and threats from surveillance systems based upon multisensor technology including combined utilization of signatures of different types. The present report aims at giving an overview of the work after the first quarter. It is based upon experience from many years of research concerning signatures, marine platforms and weapon systems at the research groups Underwater acoustics Computational physics and Magnetics at FOI.