The Institute of Historical Research: Military History Collections website has a wealth of resources for military researchers. They have a searchable catalogue of primary source materials available at the institute, a thesis collection and has links to other military history organisations and museums.
The British Commission for Military History, runs the British Journal for Military History, an open-access journal established to promote through research publication and discussion, the understanding of military history without geographical or time period restrictions. Bringing high quality research to audiences beyond academia.
The Journal of the Society for Army Historical Research, accessible on JSTOR, has issues starting from the 1920's through to 2017. This journal is considered to be one of the premier journals of military history, promoting army historical research with an ongoing commitment to publishing primary sources.
The British Military History website provides a research resources page, on the British army from 1930-1950. Use this website for links to primary research sources and websites such as The Long, Long Trail providing a wealth of information and detail on the British Army of 1914-1918. This website also has interesting links to the London Gazette where you can search for commissions, promotions and citations for gallantry medals that have been published since 1665.