The Automatic Identification System (AIS) data, which was initially conceived for collision avoidance, has increasingly been repurposed for surveillance applications. However, the intrinsic complexity and sheer volume of AIS data transmitted to base stations make humanly impossible to use it for surveillance. To mitigate this issue, we propose an unsupervised learning algorithm designed to autonomously identify anomalous instances within the AIS dataset throughout a vessel’s voyage. Given that the raw fields in AIS data are not directly applicable for training machine learning (ML) algorithms, we introduce an innovative feature extraction methodology to derive pertinent attributes essential for training the Isolation Forest. The trained Isolation Forest algorithm automatically detects the anomalous AIS instances automatically based on the extracted features. The number of instances which the officers need to be given attention is relatively very less compared to the actual AIS instances.