What is Rule B Attachment?

Legal Definition
Rule B attachments are issued under Rule B of the Supplemental Rules for Certain Admiralty and Maritime Claims of the Federal Rules of Civil Procedure. Under that provision, the court is allowed to attach a defendant's property up to the value of the suit. Although these claims are filed during in personam actions, they are in rem in nature, as the Court is attaching property to the suit. This has been described as a "remedy quasi in rem."

The Rule B procedure is in addition to the in rem procedure for arresting vessels that is available under Rule C.
-- Wikipedia