Real-time information is essential for effective operator decision making and performance in safety-critical systems, as operators must make crucial decisions quickly, utilizing relevant information to monitor, assess and respond. Research examining the impact of ultimodal displays with augmented reality (AR) on operators performing safety-critical work has shown improved operator situation awareness, but mixed results with respect to performance and workload. Multiple-resource theory (MRT) posits that individuals will experience different performance impacts when information is received using different modalities, compared to when the information is communicated using a single modality. Earlier work provides a theoretical basis for expectations about the impacts of multimodal displays, but does not address the costs or impacts of digital layers of AR imagery in multimodal displays with small viewscapes, a gap our research addresses in safety-critical systems such as Arctic search and rescue and maritime navigation.