This paper analyses the impact of home military spending and foreign military threat on economic growth in a stochastic endogenous growth model involving the supply-side and demand-side effects produced by military spending. The paper states that an increase in home military spending affects economic growth through three channels, including the crowding-out effect, the spin-off effect, and the resource mobilization effect. The net effect which depends on these three channels is ambiguous. Hence, we demonstrate that there exists an optimal defence burden that maximizes the economic growth rate. Furthermore, the optimal defence burden depends on the degree of risk preference. Namely, the optimal defence burden of the risk-loving agent is more than that of the risk-neutral agent, and in turn is more than that of the risk-averse agent. At the same time, we prove that the relationship between the volatility in military spending and economic growth also depends on the degree of risk preference. In addition, we show that greater volatility in foreign military spending leads to a decrease in home aggregate consumption, and hence speeds up economic growth in the home country.