Linq to SQL Join Statement in C#

using System;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.ServiceModel.Activation;
using System.Collections.Generic;
 
namespace SilverlightBingMapControl.Web
{
    [ServiceContract(Namespace = "")]
    [SilverlightFaultBehavior]
    [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
    public class PositionService
    {
        [OperationContract]
        List<it_position> GetAllPositions()
        {
            PositionDataClassesDataContext context = new PositionDataClassesDataContext();
 
            var result = from positions in context.it_positions select positions;
            return result.ToList();
        }
 

        [OperationContract]
        List<it_vessel> GetAllVessels()
        {
            PositionDataClassesDataContext ser = new PositionDataClassesDataContext();
            var res = from vessels in ser.it_vessels select vessels;
 
            return res.ToList();
        }
    }
}

[OperationContract]
List<it_vessel> GetAllInitialize()
{
    PositionDataClassesDataContext context = new PositionDataClassesDataContext();
 
    var res = from positions in context.it_positions
              join vessels in context.it_vessels on positions.imo_no equals vessels.imo_no
              select;
 
    return res.ToList();
}

Error   2   The type of one of the expressions in the join clause is incorrect.  Type inference failed in the call to 'Join'.   C:\Users\student\KM\SilverlightBingMapControl - 2013-02-11\SilverlightBingMapControl\SilverlightBingMapControl.Web\PositionService.svc.cs   40  23  SilverlightBingMapControl.Web
Error   3   The type arguments for method 'System.Linq.Enumerable.ToList<TSource>(System.Collections.Generic.IEnumerable<TSource>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.    C:\Users\student\KM\SilverlightBingMapControl - 2013-02-11\SilverlightBingMapControl\SilverlightBingMapControl.Web\PositionService.svc.cs   43  20  SilverlightBingMapControl.Web
Error   4   Invalid expression term ';' C:\Users\student\KM\SilverlightBingMapControl - 2013-02-11\SilverlightBingMapControl\SilverlightBingMapControl.Web\PositionService.svc.cs   41  29  SilverlightBingMapControl.Web
Error   5   ; expected  C:\Users\student\KM\SilverlightBingMapControl - 2013-02-11\SilverlightBingMapControl\SilverlightBingMapControl.Web\PositionService.svc.cs   41  30  SilverlightBingMapControl.Web