Within the marine industry high-performance materials such as sandwich composites are attractive materials for lightweight constructions. Their increasing applications for especially load-carrying purposes require an extended knowledge of possible hidden flaws incurred after fabrication or in service. Most of these defects are invisible from the outside and therefore the needs for reliable and effective non-destructive testing (NDT) methods exist. As the results of the latest development within the field of NDT on composite materials, new developed automated ultrasonic methods for large-scale inspection of sandwich structures have shown great potential in revealing these typical defects. Mainly these methods have been developed within two European projects called 'EUCLID RTP 3.21' and 'JP 3.23 THALES Project'. On basis of the successful ultrasonic developing work performed within the two projects, it has now been possible to make clear detection of defects in GRP, CFRP, PVC foam and Balsa wood sandwich structures by means of automated ultrasonic scanner equipment, especially defects located in the core material such as crushed core, core cracks and skin-core debondings. The reasons for these improvements in detection capability on sandwich structures are mainly due to pulser and scanning optimisations such as probe frequency, pulser characteristics, frequency filtering on receiver amplifier, and coupling conditions. Existing portable ultrasonic track scanner (ATS-1) for detailed inspection of large composite structures has been improved. The scanner has been enlarged and is now covering an effective scanning area of 6x0,5 m(exp2). Within the EUCLID RTP3.21 this scanner has proved to be very flexible in different inspection set-ups, from the inspection of straight and slightly curved panels to the inspection of geometrical complicated joints. Within the JP 3.23 THALES project a new 8 channel Multi Probe Scanner (MPS) has been developed and a prototype is now ready to be tested in the laboratory and on-side naval ships. This Scanner is developed for very fast spot-check inspection of large composite structures with an effective scanning time of 2,4 m(exp2)/min.