IR decoys can be an effective countermeasure against IR guided anti ship missiles. However, it's not so easy to determine how the decoys should be deployed to get maximum effectiveness. A limitation of trials is that results are obtained for the specific trial condition only. Software tools have been developed to solve these problems. One solution uses recorded IR imagery from a decoy deployment trial, while the other solution generates IR imagery and is thus independent of trials. In the first solution, a combination of hardware and software is used that allows recording of a scene with an infrared camera, and simulating a missile seeker. A pre-processing algorithm corrects the recorded images before they are fed into the seeker algorithm of the simulated missile. To perform this correction the pre-processing uses the speed, distance to the target and field of view of the IR camera as fixed parameters and the speed and starting distance of the simulated missile as variable parameters. Modtran and the Navy Aerosol Model are used to calculate the atmospheric transmission effects in the pre-processing. The second solution generates artificial IR images that are subsequently fed into the seeker algorithm. This solution also allows variation of those parameters that are fixed when recorded IR imagery is used. Examples are among others: the signature of the target ship, the orientation, size and speed of the target ship, the type of decoy, the timing of the decoy sequence, atmospheric conditions etc. With these tools the effectiveness of decoy deployment in various scenarios can be evaluated.