The Provisional Irish Republican Army (PIRA) repeatedly showed itself to be one of the most inventive and adaptive of all the violent non-state actors who operated in the latter part of the twentieth century. Among its most innovative exploits was the PIRA’s successful development and fielding – spanning almost its entire operational lifetime – of improvised mortar systems. This chapter will trace the sustained development of mortars, including the underlying motivations for pursuing mortars as a complex engineering effort, the process by which the development took place and the underpinnings of its success. The discussion will show that the PIRA’s mortar development program was born out of tactical necessity but enabled by good organizational practices and the organization’s access to materials, expertise and places in which to leverage these. Disclaimer Editor’s Note: This article forms part of a series of related case studies collected in this Special Issue and should be viewed in the context of the broader phenomenon of complex engineering by violent non-state actors. Readers are advised to consult the introductory and concluding papers for a full explanation and comparative analysis of the cases. Acknowledgements This case study was excerpted and abridged from Gary Ackerman, More Bang for the Buck (Unpublished Doctoral Dissertation: King’s College London, 2014). This work was supported by Sandia National Laboratories, Contract #1525332. Any opinions, findings, conclusions and recommendations in this issue are those of the authors and do not necessarily reflect views of Sandia National Laboratories or the U.S. Department of Energy. This article is available in Journal of Strategic Security: http://scholarcommons.usf.edu/jss/vol9/iss1/4 This article is available in Journal of Strategic Security: http://scholarcommons.usf.edu/jss/vol9/iss1/4