The latest developments in AlGaInN laser diode technology are reviewed. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v. to the visible, i.e., 380-530nm, by tuning the indium content of the laser GaInN quantum well. Of specific interest for defence applications is blue-green laser diode technology for underwater telecommunications and sensing applications. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW in the 400-420nm wavelength range with high reliability. Low defectivity and highly uniform GaN-substrates allow arrays and bars of nitride lasers to be fabricated. In addition, high power operation of AlGaInN laser diodes is demonstrated with the operation of a single chip, ‘mini-array’ consisting of a 3 stripe common p-contact at powers up to 2.5W cw in the 408-412 nm wavelength range and a 16 stripe common p-contact laser array at powers over 4W cw.