Converts unsaturated trans-2-enoyl-CoA species ((2E)-enoyl- CoA) to the corresponding (3S)-3hydroxyacyl-CoA species through addition of a water molecule to the double bond (PubMed:25125611, PubMed:26251176). Catalyzes the hydration of medium- and short-chained fatty enoyl-CoA thioesters from 4 carbons long (C4) up to C16 (PubMed:26251176). Has high substrate specificity for crotonyl-CoA ((2E)-butenoyl-CoA) and moderate specificity for acryloyl-CoA, 3- methylcrotonyl-CoA (3-methyl-(2E)-butenoyl-CoA) and methacrylyl-CoA ((2E)-2-methylpropenoyl-CoA) (PubMed:26251176). Can bind tiglyl-CoA (2- methylcrotonoyl-CoA), but hydrates only a small amount of this substrate (PubMed:26251176). Plays a key role in the beta-oxidation spiral of short- and medium-chain fatty acid oxidation (PubMed:25125611, PubMed:26251176). At a lower rate than the hydratase reaction, catalyzes the isomerase reaction of trans-3-enoyl-CoA species (such as (3E)-hexenoyl-CoA) to trans-2-enoyl-CoA species (such as (2E)- hexenoyl-CoA), which are subsequently hydrated to 3(S)-3-hydroxyacyl- CoA species (such as (3S)-hydroxyhexanoyl-CoA) (By similarity). {ECO:0000250|UniProtKB:P14604, ECO:0000269|PubMed:25125611, ECO:0000269|PubMed:26251176}. This is the function of ECHS1 (enoyl-CoA hydratase, short chain 1, ENSG00000127884).