MARitime SIMulated (MARSIM) is a comprehensive and labeled dataset created to test and evaluate NMEA-based anomaly detection approaches related to GNSS/GPS spoofing attacks in the maritime context, e.g. MANA. It consists of multiple scenarios (benign and attacked) with a duration of 120 s, provided as network traffic recordings, i.e., in packet capture (pcap) format. Each recording contains the NMEA 0183 sentences transmitted within the network of a single vessel heading north from a fixed point with constant velocity. The recordings are reduced to two PNT transmitting devices, namely the pair of GPS receivers, which are placed at a fixed distance of 4 m from each other. Working with the provided packet captures can be facilitated by using our Wireshark dissector. For more information, please see Spravil J, Hemminghaus C, von Rechenberg M, Padilla E, Bauer J. Detecting Maritime GPS Spoofing Attacks Based on NMEA Sentence Integrity Monitoring. Journal of Marine Science and Engineering. 2023; 11(5):928. DOI: 10.3390/jmse11050928