Submarine periscopes are moving from analog to digital, but there is a lack of empirical evidence regarding the relative advantages that different digital human–machine interface configurations might provide to the operator. We experimentally compared the effectiveness of two digital concepts for displaying and analysing periscope imagery during a simulated submarine mission. OPTIX modelled a traditional periscope by presenting a narrow (20° horizontal arc) rotating image of the horizon. OPTIMUS displayed the full 360° panoramic representation of the horizon and was augmented with digital analysis tools. OPTIMUS supported faster and more accurate performance by participants (N = 32) and lowered perceived workload, compared to when the same participants used OPTIX. However, time taken to respond to situation awareness queries and awareness of one’s own performance (meta-awareness) was poorer when using OPTIMUS. OPTIMUS holds an advantage in that it can improve performance whilst reducing workload, but the SA and meta-awareness decrements are potentially problematic.