Which are the other sub-fields of underwriting field?

Is insurance underwriter a single category under underwriter or are there any other fields available too?

Underwriting is a wide area which has many variations and all of these variations involve different kind of work. So you should be very clear as to which field you need to opt for before taking the next step of making up your mind to do enter that particular field of underwriting. There are main four categories that are there under the main category of underwriter: Life Insurance, Health Insurance, Mortgage Insurance and Property/casualty insurance. Life and health insurance underwriters may still go further and specialise in group or individual policies. Property and casualty underwriters generally specialise in either commercial or personal insurance and then by the type of risk insured, as in fire, homeowners, automobile, marine or liability insurance, or workers’ compensation. An insurance professional who is responsible for evaluating the risk of mortgage application, from the financial institutions’ perspective is called as a mortgage underwriter. They are basically employed by financial or banking institutions. There are a couple of new fields that come under the major field of underwriting i.e. Construction and Marine underwriters who frequently travel to inspect worksites and assess risks.
Underwriters are the people who work in insurance agencies or for organisation that offer insurance services to insurance companies and policyholders. Mortgage companies, banks and real estate firms also offer jobs to a small number of inexperienced or newly qualified underwriters. Experienced underwriters may get promoted as a senior underwriter or underwriting manager positions in their respective firms. You can move into the core areas of insurance like, risk management, broking, etc after you have gained sufficient experience as an underwriter. If you know how to speak a foreign language then there is a possibility that you might get a chance to work abroad.