This report is the result of a limited study of fiber laser sensors in defence applications. Fiber laser sensors have characteristics such as extreme strain sensitivity and small size which are useful in certain military applications. Among these, towed array sonar systems for underwater surveillance have been found to be of special interest and this report focus on aspects related to hydroacoustics. The potentially very lightweight and small-size sensor cable, including up to 100 acoustic elements should be useful not only in special applications within this field but also generally in various kinds of towed array applications. A comparably short, approximately 5 cm, single polarization distributed feedback fiber laser sensor element seems to be the most promising configuration for the hydroacoustic task. A distributed Bragg resonator is also a possible configuration enabling a much longer cavity with reduced noise figures and with an extended gauge length, (useful for flow noise reduction), but to the cost of more elaborate frequency interrogation. The fiber laser cavities, being the sensor elements responding with an optical frequency change to strain, are coated with elasto-plastic materials to provide acoustic gain (potentially up to 50dB). They can be serially pumped through the fiber core by means of conventional semiconductor pump lasers with output powers around 100 mW. Several elements can be cascaded, seemingly without degrading the system noise properties. Frequency noise, relative intensity noise and dynamic range have magnitudes which allow for threshold acoustic detection close to the desired levels, i.e. below the ambient acoustic noise of a calm sea (sea state zero). Potential problems of the technology include, polarization and longitudinal mode beating, hole burning effects and back scattered light leading to laser instability.