Java: Searching through 2D array for multiple values

Ok i created a board that can have two types of ships, S and M, however, I want java to show me different messages whenever the board either contains only S but no M or only M but no S or when both are present. I am not able to do that. Please do help. This is what i have tried so far

import java.util.ArrayList;
import java.util.Scanner;


public class bord {
    public static void main(String[] args) {
        String Board[][]= new String[4][4];
        int n=0;
        for(int i=0;i<4;i++)
        {
            for(int j=0;j<4;j++)
            {
                Board[i][j]="-";

            }
        }
        for(int i=0;i<4;i++)
        {
            for(int j=0;j<4;j++)
            {
                System.out.print(Board[i][j]);
            }
            System.out.println();
        }
        System.out.println("_______________");

             //from here!
        Board[1][1]="S";
        Board[3][2]="M";

        int a=0;
        for(int i=0;i<4;i++)
        {
            for(int j=0;j<4;j++)
            {
                if(Board[i][j].equalsIgnoreCase("S") && !Board[i][j].equalsIgnoreCase("M"))
                {

                    a=1;

                }
                else if(Board[i][j].equalsIgnoreCase("M") &&  !Board[i][j].equalsIgnoreCase("S"))
                    {
                        a=2;

                    }
                else if(Board[i][j].equalsIgnoreCase("S") || Board[i][j].equalsIgnoreCase("M") )
                        a=3;

            }

        }
        if(a==0)
        {
            System.out.println("No ship found");
        }
        else if(a==1)
            System.out.println("Found it");

    else if(a==2)
        {
        System.out.println("Found it yet again");
        }
    else
        System.out.println("keep playing again");
    }
}