First Vikings had the standard US NAVY schemes with Federal Standard colour FS16440 Gull grey and white FS16875 under surfaces. Later on, overall grey Vikings appeared. Weathering also is quite apparent depending on their service career and colour painting maintenance state. 

Over 20 years ago, I once made the Hasegawa S-3A kit (see pictures at end of page). Now I decided add another Viking and to do a simple build of the US-3 COD version, of which Hasegawa issued kit no. K-23. 
COD kit
The main difference between the kits are only in the decals and you have to "paint over" or fill the small windows immediately aft of the cockpit. For the US-3 you also get a pair of big travel pods for under the wing and a "clean" lower rear part where normally the sono boy chutes are.  

  one of the older boxes of the Hasegawa S-3

Instructions are clear with Gunze Sanyo colours. The COD kit has attractive decals for 2 schemes:

Gullgrey / white VS-33 Screw Birds
Overall white VRC-50 COD 

The decals are OK, except for the too blue' ish US Stars-and-bars, these were replaced with better ones from CAM decals.

All Hasegawa kits have raised panels lines but there are fine and the kit fits reasonably well. The only thing is that ejector pin marks are in awkward places, like the insides of the engine intakes and insides of wheel doors.

I would keep the raised panels, which are fine enough and not very disturbing.The overall airframe only needed some filler at the wing-fuselage joints and some sanding at mating surfaces, so the panel lines are not really damaged going along. 

Aft of the cockpit there is no detail and it has no weapons bay nor the option to have the outher wings folded. On the other hand it has separate trailing edge flaps. 

So I first started with basically assembling the airframe. Cockpit detailling was left for later on, I only added the cockpit tub.

The cockpit is sparsely detailed with very simple ESCAPAC seats and no side consoles. For the instruments decals are provided. The Vikings had tinted glass and this is in the kit, but still a lot of detail can be seen. 

The horizontal stabilizer were left off as well for easier handling.

The engine intakes have ejector pins marks, I decided to cover the intakes with protecting plates made from thin metal household foil  later on. Of one of the external US-3 pods, I cut open the doors to add some interest. Also, some minor detail was added inside the bare wheel bays. The engine pods and transport pods were kept separate, to be painted in one go but not yet attached.

Now a little putty filling and sanding was done and when that was OK, the small antennas were added. Next, the overall model got a coat of matt light grey to check for any flaws with the airbrush. 

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This particular US-3 COD Viking scheme is overall white, so next steps was a coat of matt white that was easy enough. Over the mat surfaces, a final coat of gloss white was added. 

Also, the various bits of the undercarriage parts and the flaps got coats of white paint going along. 

A lot of work are the buff coloured bits of anti-icing on various leading edges of wings, tails and stabilizers. These were masked off with TAMIYA masking tape and sprayed. The inner flap sections were painted red after being masked of as well. 

Now the overall model was in fact ready for decalling, this would be easier now and prevent damaging the model. A couple of coats of Johnson Kleer/Pledge were added to prevent silvering and the kit decals added. 

The decals went on fine, except for the travel pods decals, needed amounts of decal softener. The US Stars-and-bars came from CAM decals. I also added a couple of cut-out dark grey decals for the escape areas above the mission crew members aft of the cockpit. 

After decalling was done, the rest of the model was to be completed. 

The cockpit area was detailed with some seat straps (you could add resin ESCAPAC seats available from eg. Pavla or others). Also added were tiny bits of equipment made of stretched sprue and rod and painting the lot. The main color in the cockpit area was mid grey with black details. 

Fortunately, the cockpit glass fits OK, only needing white glue to close the gaps. The glass framing were hand painted black. 

The wheel undercarriage was now added and these went on fine complete with their doors. I added a few brake wires on the gear legs. The stabilizers, engines and travel pods were now set on the model. 

Tiny bits were now only left to add, like a couple of windscreen wipers made from thin stretched sprue and navigation lights on top of the fuselage and wingtips. 

The grey emergency ejection panels aft of the cockpit were cut out from grey decal. 
Only some minor "wash" was added to the model, particularly on the aileron gaps and rudder.
Finally , the model got a "protecting" coat of Johnson Future/Pledge. 

The result is fine.

 note the slightly lowered trailing edge flaps

travel pod

 the black areas at the travel pods ends were hand painted

  a view "on deck". 

A nice US NAVY model is now in the collection with relatively limited effort.