Before giving any answer, we need to know what's the chemical composition of this steel. Do you know who the manufacturer is? The name suggests that it's what's called a "proprietary alloy".
Giovanni S. Crisi
Sao Paulo - Brazil

The Navy developed Hy80 and HY100 for Subs. Its a CrMo material with some Ni thrown in to with stand temp changes.
You forgot to mention what process you plan to use. SAW,GMAW,SMAW or GTAW.
If you need "CERTIFICATION" you need to do a PQR on what ever spec you get or write. Dont belive you find one in AWSD1.1
Hy80 is a hardenable material and needs a preheat and depending on your application a PWHT. For fillers look up E9018 for SMAW and for bare wire I suggest you go for ER120S-1. Lot of over kill but I dont know your application.

The MIL-S-16216 HY-80 is a quenched and tempered steel (Q&T) with specified yield strengths betwen 80000-100000PSI and an excellent toughness. In welding any material the goal is produce a weld metal with properties almost the same as those of th base metal. You can match the yield strength of the HY-80 using E9018 (like Mr. Ron said you) or E10018, but there are another filler metals that you can use according your service conditions. The really difficult thing is match the toughness value of HY-80 in the as-weld condition; remember that the excellent notch toughness has been obtained by heat treatment (Q&T) and you may to do the same in your weld metal for match impact properties how was said yet by Mr Ron. I advise you to get more study about this material and the service requirements of your weldments. You can find some information about it in this book: Analysis if welded structures-Residual stresses, distortion and their consequences by Koichi Masubuchi (Massachusets Institute of Technology).

Jorge Giraldo
Medellín, Colombia

I would strongly suggest for you to contact the NJC (Navy Joining Center) . I worked at Electric boat up in Groton CT back in 1978 and, I must've welded about ten miles worth of HY-80 !!! If anybody knows, they will!!! If you have trouble finding this organization and you are a member of the AWS, you should be able to find it in the monthly issue of the journal.

The material HY 80 is composed of the following chemistry the material number according to the Register of European Steels 9th Edition.

Material No.: 1.6780 : 15NiCrMo10-6

C, Si, Mn, P, S, Cr,
.12-.16, .15-.35, .10-.40, <.010, <.010, 1.0-1.8,

Mo, Ni, V, Cu, Ti
.20-.60, 2.0-3.25, <.03, <.25, <.20

Thyssen Stahl AG Werk Krefeld - Germany
Thyssen Stahl AG - Germany
Vereinigte Schmiedewerke GmbH- Germany

If you would like to weld this material using an efficient method, you should consider seamless flux cored wires such as MEGAFIL 742B (E 110 T5-K4 basic slag system) MEGAFIL 742M (E111 T1-K4 slag free metal cored). Both of these products are favored by manufactures of cranes, steel construction, foundries, and earthmoving equipment. The weld is extremely crack resistant and the seamless flux cored wire is impervious to moisture pickup. If you are considering a high strength weldment with x-ray requirements you should evaluate these products.