Trying to randomly place "ships" on a matrix for a game of battleship, running a loop to stop ships from overlapping but it continually tells me "index exceeds matrix dimensions", any pointers on how to execute the loop properly would be appreciated

function  M = AddShip( Matrix, length1)

M=Matrix;

%SHIP1--CRUISER(22)
loop_on=0;

while loop_on==0

%%%generate randomn number, gives either vert or horiz direction%%%
direction=rand(1);
if direction <=0.5
    direction='vertical';
elseif direction>0.5
    direction='horizontal';
end

%%%Generate randomn starting point for SHIP1-Destroyer(22)%%%
StartRow1=randi(10);
StartCol1=randi(10);

%%%if the sum of the numbers on the matrix is greater than 0 there is
%%%already a ship there, so code must run again until a suitable place is
%%%found %%%
if     strcmp(direction,'vertical')==1 && sum(M( StartRow1, StartCol1:StartCol1+1 ))>0 
elseif strcmp(direction,'horizontal')==1 && sum(M( StartRow1:StartRow1+1, StartCol1))>0
    loop_on=0;
else loop_on=1;

end

while loop_on==1
if strcmp(direction,'vertical')==1 %if vertical add to the column
   M( StartRow1, StartCol1:StartCol1+1 )=22;
elseif strcmp(direction,'horizontal')==1 %if horizontal add to the row
   M( StartRow1:StartRow1+1, StartCol1)=22;

end
end

end
%%%repeat for the other 4 ships%%%