This paper investigates four questions related to ethical issues associated with the involvement of engineers and scientists in 'military work', including the influence of ethical values and beliefs, the role of gendered perspectives and moves beyond the purely technical. It fits strongly into a human (and planet)-centred systems perspective and extends my previous AI and Society papers on othering and narrative ethics, and ethics and social responsibility. It has two main contributions. The first involves an analysis of the literature through (...) the application of different ethical theories and the application of gendered analysis to discussion of masculinities in engineering and the military. The second is a survey of scientists and engineers to investigate their opinions and experiences. The conclusions draw together the results of these two contributions to provide preliminary responses to the four questions and include a series of recommendations covering education and training, ethical approval of work not involving human participants or animals, the need for organisational support, approaches covering wider perspectives and the encouragement of individual ethical commitment. (shrink)